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CHAPTER ONE

THE DIGESTIVE SYSTEM - Deals with the intake, physical breakdown, chemical digestion, & absorption of food, along with the elimination if waste products created by the process. The digestive system also eliminates certain toxic substances & secretes hormones it uses to regulate itself.

THE ORAL CAVITY - aka mouth, consists of lips, teeth & gums, tongue, oropharynx, & the associated salivary glands. The lips are a zone of transition from the skin of the face to the mucous membrane (a general term denoting the surface of an organ lubricated by moisture) lining the gums & the inside of your cheeks. Several layers of muscle help lips grab & retain food & water within mouth. Grazing animals like cattle, sheep, & horses have muscular lips that are prehensile (i.e., adapted to gasp plant material).

TEETH - Most "specialized" of organs within the mouth. The crown is visible portion of the tooth, beyond the gum line & embedded in the jaw is the root, some teeth have two or more roots, between the root & crown some teeth have a slight narrowing called the neck, which is approximately where the gums attach to the tooth. Inside each tooth you'll find three or four layers of tissue. The inside layer, or core, of each tooth is called the pulp & contains connective tissue, blood vessels, & nerves. Covering the pulp is a material called dentin, an inorganic (nonliving) material somewhat like inorganic material in bone that constitutes the bulk of the tooth. Enamel is the outermost layer of the tooth. The inorganic substance is extremely hard & arranged in parallel rods cemented together with a calcified inorganic substrate. Enamel is the hardest substance in the body, despite this, enamel is somewhat translucent. The tooth's root is embedded into a jaw socket called an alveolus by naturally occurring cement that forms a fourth layer over the roots. Plaque is bacteria & salivary material that can accumulate at the junction of the gum & tooth. The teeth of horses & cheek teeth (premolars & molars) of ruminants (herbivores, like cows, sheep & goats) are constantly growing. Occlusion refers to where upper & lower teeth meet & touch. Factors that affect this process are: (1) The way the upper & lower teeth come together, (2) How that animal chews, & (3) How fast the individual teeth erupt. as a result, the teeth may develop sharp edges that become painful to the lips & gums when the horse chews. Tis requires the teeth to be floated, a process in which a file is used to grind the sharp edges of the teeth down enough to make them less painful. Teeth in most animals come in two sets: a deciduous (temporary or "baby") set & a permanent set. Deciduous teeth usually below the gum line but erupt within three months to three years depending on species. Permanent teeth develop in the alveoli of the bone before eruption. Retained deciduous tooth, is an abnormal condition in which the deciduous teeth isn't shed. Most domestic animals have four types of teeth, which are arranged in two arches called dental arcades, one on the upper jaw & one on the lower jaw. The four teeth types are:

Incisors (to cut food)

Canines (to tear food)

Premolars (to grind food into smaller particles for swallowing)

Molars (to grind food into smaller particles for swallowing)

You'll find all four types of teeth in carnivores, horses, & pigs. Ruminants lack upper incisors & canine teeth. As mentioned ruminants lack upper incisors: Instead a dental pad consisting of hardened mucous membrane tissue is present in the rostral upper jaw opposite the lower incisors.

TONGUE - Is a muscular organ used for manipulating food within the mouth. The interior of the tongue is composed of many interlocking muscle bundles. The muscle fibers bundles are held together by connective tissue.

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CHAPTER 2 CONTINUED.....

Tongues surface is covered with squamous epithelial tissue just like the rest of the mouth, but on the surface of the tongue are small projections called papillae that help tongue control food, some are specifically modified to carry the taste buds. Salivary glands are located throughout the oral cavity, these glands are very small, consisting of a cluster of cells that produce saliva & a small tube called a duct, which carries the saliva from the secreting cells to the oral cavity's surface. Accessory salivary glands, are smaller & secrete saliva in a continuous manner to keep surface of tongue moist. Three pars of larger salivary glands exist:

Parotid salivary glands--located in the angle between the ear & the back of the lower jawbone.

Submandibular (aka mandibular) salivary glands--located just inside & forward of the parotid salivary glands between the caudal borders of the mandibles.

Sublingual (aka lingual) salivary glands--located beneath the tongue.

Saliva performs the following functions:

Moistens the food to make it easier to chew & form a bolus (rounded mass of food)

Keeps the lining of the oral cavity moistened

Brings food particles in contact with taste buds

OROPHARYNX/PHARYNX - Opening at the back of the throat. Muscular walled area that opens to both the digestive system & the respiratory system. The pharynx (throat) opens into the nasal cavity, the oral cavity, the esophagus, & the trachea. Pharynx serves as a conduit to transport food & liquid from the oral cavity to the esophagus & air from the mouth or nasal cavity to the trachea. There are four layers of the basic "tube" of the intestinal tract. Food moves through the center lumen of the tube. The innermost layer adjacent to the lumen is the mucosal layer that's comprised of epithelial cells. The next layer is the submucosa, which contains glands & connective tissue. Third layer is the muscle layer that makes movement possible. The outermost layer is the serosa, which is a thin, tough layer of connective tissue. The basic anatomy of this tube is similar for all the segments of the intestinal tract-- the esophagus, the stomach, the small intestine, & the large intestine.

THE ESOPHAGUS - Basically a muscular tube that transports food from the pharynx to the stomach. The bulk of the esophagus consists of muscle tissue that contracts in a coordinated fashion to push food in the distal direction. It accomplishes this task by contracting one area while relaxing an adjacent area; Process known as peristalsis. The lining of the esophagus is stratified squamous epithelium that's fairly resistant to physical trauma from food & foreign objects that are swallowed. Esophagitis (inflammation of the esophagus) occurs when acid from stomach refluxes repeatedly to the esophagus. Scar tissue may form, leading to constriction of the esophagus called esophageal stricture: strictures make passage of solid materials difficult. Megaesophagus can occur in some dogs, cats & humans, in this condition, the muscles of the esophagus fail to contract. The asophagus has two muscle sphincters, which are rings of muscle surrounding an opening. with one at each end of the esophagus, they keep food from flowing out of the esophagus. The sphincters aren;t "foolproof".The serosa is a thing tissue layer that covers the entire gastrointestinal tract, including the esophagus, stomach, small intestine, & colon (continuous tissue). blood vessels, nerves, & lymphatics run through the serosa.

THE RUMINANT (COMPOUND) STOMACH

Are animals that swallow their food & then regurgitate it back through the esophagus into the mouth to chew on it again before swallowing it once more. This process is called "rumination" Ruminants have more complex stomachs. they have one stomach with four compartments. These are:

Reticulum

Rumen

Omasum

Abomasum

The first three compartments are sometimes collectively CALLED THE "FORESTOMACH (OR PRESTOMACH)". tHE RETICULUM IS THE SMALLEST & MOST CRANIAL PART OF THE RUUMINANT STOMACH.

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CHAPTER TWO..

The rumen is the largest part of the forestomach & takes up most of the abdomen's left side. most important part of the reuminant stomach, because it's where fermentation occurs. In the process of fermentation, bacteria & protozoa as well as enzymes act on plant material to break down cellulose (the primary component of plant fiber) into volatile fatty acids (VFAs), proteins, & vitamins. By-products of fermentation, such as carbon dioxide & methane gases, are also released; these by-products must be released either through the mouth or anus. The rumen also digests bacteria & absorbs the breakdown products of both cellulose & bacteria. The omasum is a ball shaped cavity with many muscular folds. VFAs that aren't absorbed in the rumen are absorbed in the omasum. Bicardonate ions & some water are also removed from the ingesta (food & drink taken into the stomach) in the omasum.The abomasum, also known as the true stomach is similar to the simple stomach of nonruminant animals in organization & function. Both omasum & abomasum lie on the right side of the abdomen.

THE MONOGASTRIC STOMACH

Similar to the esophagus in basic tubular anatomy, but similarity ends there. The stomach begins the process of digestion in earnest, mixes the food with digestive fluids & stores food until it has been digested into particles small enough to enter the small intestine. Thus, the stomach differs from the esophagus in the following three ways:

The stomach can expand to much larger diameter than the esophagus, so the stomach's capacity to store food is much greater.

The muscular layers of the stomach differ from those of the esophagus because the stomach must not only eventually propel food in the distal direction, but also churn & mix the food that's being stored in it. The stomach has an additional muscle layer, called the oblique layer, to accomplish this.

The mucosa of the stomach consists of a variety of glandular epithelial structures that secrete digestive fluid, mucus, & acid.

The human stomach's mucosa has many folds called "rugae". simple stomachs are roughly J-shaped, the human stomach is similar to that of the dog, cat, pig, & horse.

A simple stomach is essentially a large, dilated tube containing the following regions

Esophageal region

Cardia

Fundus

Body

Pyloric antrum

Pylorus

The esophageal region of the stomach lies most cranial & contains the cardia, a small area near the opening of the esophagus. Just caudal is the cardiac region, which contains mucous glands that secrete mucus but not digestive enzymes. The bulk of the simple stomach consists of the next region of fundus. This region contains most of the gastric glands, which ae the digestive glands that secrete a variety of substances to chemically break down food. The body is a glandular, distensible area, & the pyloric antrum functions to grind food & control the amount of hydrochloric acid produced. The pylorus, helps retain food in the stomach until that food is sufficiently digested to enter small intestine. Mucus layer covering stomach's surface prevents mucosa from being damaged by the acid & pepsin in the gastric juice. Ulcer is decreased or hydrochloric acid production increased this protection may break down.

The pyloric antrum has glands that primarily secrete mucus & a hormone called gastrin. Gastrin has three major functions:

Stimulates the production of hydrochloric acid & pepsin in the stomach

Stimulates contraction of stomach muscles to increase stomach emptying

Decreases pyloric tone to allow food to enter the small intestine

GASTRIC MOTILITY & SECRETIONS

The digestive process in nonruminants iis similar to the process of humans. food enters stomach and is exposed to gastric juice (contains mucus from cells in almost all areas of the stomach), digestive enzymes such as pepsin from peptic cells in the gastric glands of the fundus & body and hydrochloric acid from parietal cells in the gastric glands. Pepsinogen secreted from the peptic cells isn't active eenzyme however once it enters the stomach lumen it's exposed to stomach acid, which converts it to pepsin, it's active form. Pepsin attacks protein molecules in food & breaks them into peptides & polypeptides.

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CHAPTER 1

Hydrochloric acid, which plays an important role in digestion, functions to

Activate pepsinogen to pepsin

Act as an antimicrobial chemical to partially sterilize the stomach

Further break down the food into smaller particles

Gastrin is secreted by mucosal cells in the stomach's region in response to presence of food in the pylorus, stimulates secretion of hydrochloric acid & pepsin, increases stomach contractions to promote emptying of stomach, & decreases the tone of the pyloric sphincter to allow food to pass.

THE SMALL INTESTINE - Three major divisions are: jejunum, ileum, & duodenum. Each of these structures has the general tubular arrangement already described, including a mucosa, submucosa, muscularis, & serosa. shaped into small folds called "villi". Columnar epithelial cells also called enterocytes are tall, thin cells lining the surface of the villi. these cells have small finger-like projections on their surface called "microvilli" which create the appearance of a "brush border" on the villus. Inside the villi are small blood vessels & lacteals, small lymphatic vessels that help absorb certain fats from the diet. In depressions between the villi, called crypts, new cells are constantly produced to replace cells lost from the tips of the villi. as cells are shed, the cells lining the sides of the villus are pushed toward the tip of the villus by new cells made in the crypts.

Interspersed with the enterocytes, which perform the digestive & absorptive functions, are goblet cells. Digestion is both physical & a chemical process. Digestive juices perform a chemical breakdown of the food into basic nutrients that the body can absorb into the bloodstream. The three most basic nutrients used by almost all animals are:

Proteins

Carbohydrates

Fats

Proteins are composed of building blocks called "amino acids", these link end to end or side to side to form peptides. peptides in turn link together and form polypeptides. carbohydrates are formed from monosaccharides. two can belinked together to form disaccharide. Triglycerides, the building blocks of fats are composed of an alcohol molecule (glycerol) bound to three fatty-acid chains. The process by which the carbon bonds are broken is called "hydrolysis" & this is the most basic process of digestion.

Enzymes are proteins produced throughout the body, they perform a variety of functions involving the manipulation of other molecules. in digestion system enzymes are essential to the chemical digestion of food,produced by glandular tissue in various parts of the digestive system, including the salivary glands, stomach, & intestine, &accessory organs such as pancreas.

Digestive enzymes recognize specific molecules or types of molecules in food & act upon those molecules to perform hydrolysis. The three categories of enzymes in the digestive tract are:

Proteases--break down proteins

Lipases--break down fat molecules

Amylases--break down carbohydrates

Enzymes are present in the cell membrane of the enterocytes lining the mucosa. These enzymes digest food particles that come in contact with thmcosa but have no effect on particles floating free in the lume. damage to the mucosa can lead to poor digestion because of damage to the cell membranes & the associated enzymes. The majority of digestion & absorption of food in dogs, cats, & pigs occur in the small intestine.

LARGE INTESTINE - Has three main parts: colon, rectum & anus.

Several organs lying near the gastrointestinal organs aid in the digestive process. These include the

Pancreas

Liver

Gallbladder

Biliary ducts

The organs secrete, store, or transport substances that promote digestion, lubricate food, & aid in food absorption.

self-check chapter one on page 27

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CHAPTER TWO FOR REALLLL...

THE REPRODUCTIVE SYSTEM - Fertilization occurs when the spermatozoa penetrates the ovum.

MEIOSIS - Reproductive cells undergo a type of cell division known as meiosis. Results in the formation of gametes (ova & spermatozoa). The processes that lead to gamete formation provide for genetic variation in a population as well as maintenance of the correct number of chromosomes in the offspring. The end result of meiosis is four daughter cells that are all genetically different from each other as well as the parent cell. Each of the four daughter cells has one-half of a chromosome pair, or one chromosome (haploid). One of the pairs of chromosomes that make up the diploid (having two sets of chromosomes) chromosome number is the sex chromosomes, these are genes that determine gender. In mammals, cells of males contain one X & one Y chromosome. Female mammals have two X chromosomes. Spermatogenesis is the process that results in formation of spermatozoa. Cells called primary spermatocytes undergo meiosis, producing two new haploid cells (secondary spermatocytes). These cells then undergo mitosis (cell division for growth) & further development that results in the mature spermatozoa. Mature spermatozoa are long cells with a head & a tail, the head contains the nucleus & is covered with an acrosome, a cap-like structure containing enzymes. The mid piece contains large numbers of mitochondria that provide energy for the cell. the tail region contains muscle-like fibers that propel the cell forward.

Oogenesis is the process that results in the formation of the ova. Female mammals are born with a fixed number of cells known as primary oocytes, they mature & are released during the animal's ovarian cycle, as with spermatogenesis, the cell initially undergoes meiosis followed by mitosis. The end result of the oogenesis is formation of one ovum & three polar bodies which contain haloid chromosome numbers but very little cytoplasm (by-products of ovum development that won't develop further)

THE MALE REPRODUCTIVE SYSTEM - Primary organs of the male reproductive system are the testes, which produce spermatozoa & male sex hormones called "androgens." Most mammals testes are located within a sac of skin called the "scrotum." Connective tissue layers known as the "vaginal tunics" surround the testes, spermatogenesis occurs in an area of the testes known as the "seminiferous tubules." While the immature spermatozoa are developing, they're attached to "sertoli cells" that provide nutritional support & protection for them. A system of ducts within the testes flows from the seminiferous tubules to the "epididymis". Spermatozoa are transported through these efferent (conveying away from a center) ducts to the epididymis for further maturation & storage until ejaculation. When ejaculation occurs, the epididymis propels the spermatozoa into the urethra, thus the urethra function in both urinary & reproductive systems. The spermatozoa are mixed with secretions from accessory reproductive organs that enter the urethra, these are: seminal vesicles, prostate gland, & bulbourethral gland. Resulting mixture is semen, containing spermatozoa mixed with nutrients & electrolytes from the accessory organs. male breeding organ: penis. The urethra runs in the middle of human penis, in canines (& few known species) the urethra is located in a groove of bone called the "os penis" The three main parts of the penis are the roots, body, & glans. The prepuce is the outer covering of the penis that's composed primarily of skin. The roots are bands of connective tissue that attach the penis to the pelvis, the body of the body consists of erectile & connective tissue. Sinuses within the erectile tissue fill with blood to create an erection. the structure & appearance of the glans of the penis vary in different species. The surface of the glans contains a large number of sensory nerves. The penis of canine species also contains a unique structure known as the bulb of the glans. This structure becomes engorged with blood during breeding. The resulting swollen bulb is held in place by the muscles of the vagina & vulva. The result is that the male can't withdraw the penis for some time after ejaculation until the swelling of the bulb subsides.

THE FEMALE REPRODUCTIVE SYSTEM - The main reproductive organs of the female are the ovaries, oviducts, uterus, & vagina; these organs are located within the dorsal part of the abdominal cavity. The ovaries containfollicles that form the site of oogenesis, they also contain endocrine cells that produce groups of hormones known as "estrogens & progestions." The process of oogenesis occurs in a cyclical fashion influenced by hormones from the anterior pituitary gland. The cycle is initiated when follicle-stimulating hormone (FSH) triggers the ovary to begin development of one of the ovarian follicles. The oocyte cells, begin to multiply & produce estrogens. oogenesis occurs as peak estrogen secretion is reached. The follicle then ruptures, releasing the mature ovum into the oviduct. "Ovulation" (release of the ovum from the follicle) occurs only after breeding/ Species that are "multiparous" (Producing several offspring or ova at one time) release many ova from each activated follicle. After ovulation, the granulosa cells multiply again & form a structure known as the "corpus luteum" (yellow body). The cells of the corpus luteum secrete a group of hormones known as "progestins.", these function to maintain pregnancy if the ovum is fertilized. The ovum that's released from the mature follicle makes its way to one of the paired oviducts (fallopian tubes). The oviducts aren't physically connected to the follicles, instead, they contain a structure known as the "infundibulum" that sevres to catch the ovum & direct it down the oviduct toward the uterus. Fertilization normally occurs within the oviducts, when the fertilized ovum reaches the uterus, its implanted into the uterine wall & then begins to develop into an embryo.

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CHAPTER TWO CONTINUED..

The uterine wall is composed of three layers of tissue: the endometrium, the myometrium & the perimetrium. The cervix I the sphincter muscle that serves to seal the uterus from the outside environment. The cervix opens at specific times during the animal's ovarian cycle to allow semen to enter from the vagina & during "parturiation" (the process of giving birth). The vagina is a muscular tube that stretches to receive the semen during the breeding & allows the passage of the offspring at birth. The portion of the female reproductive system that's visible externally is the "vulva" is composed of the vestibule, clitoris, & labia. The vestibule is the space between the opening of the vagina & the labia, The urethra opens onto the floor od the vestibule, the clitoris is a small erectile bdoy located within the vestibule, the external boundary of the vulva is the labia (lips of the vulva)

THE ESTROUS CYCLE - The time from the beginning of one reproductive cycle to the next is referred to as the "estrous cycle." Hormones from the anterior pituitary gland, FSH & luteinizing hormone (LH), control the events that occur during this cycle. Canines are diestrous, meaning they have two estrous cycles each year, cattle & swine are polyestrous species that cycle continuously throughout the year, monoestrous species have just on reproductive cycle each year. Some species (the cat, horse, & sheep) are seasonally polyestrous. this means that during certain times of the year, usually spring & fall females cycle continuously. The estrous cycle can be divided into specific stages, each with it's own physiological & behavioral characteristics. The stages are proestrus, estrus, metestrus, & dietrus. During proestrus, the follicle begins to develop. The linings of the oviducts, vagina, & uterus start thickening. A process called "cornification" also occurs in the epithelial lining of the vagina. The squamous epithelial cells that make up the vaginal wall become angular & anuclear (without a nucleus) as a protective keratin layer forms on their surface. Estrus is the period during which the feale is sexually receptibe to the male. The start of the estrus is concurrent with the peak of estrogen production. Estrus ends whe ovulation occurs. Metestrus is the period during which the corpus luteum (yellow body is formed. Diestrus begins when the corpus luteum is at it's maximal size. reproductively inactive stage known as anestrus. Species that are monoestrous or seasonally polyestrous exhibit anestrus, whereas polyestrous animals don't.

FERTILIZATION - Copulation (act of breeding) females allow it only during estrus phase of the ovarian cycle. copulation triggers the release of the hormone "oxytocin" from the posterior pituitary of the female, this acts to cause contraction of the female reproductive tract. Capacitation is a process that activates the spermatozoa to penetrate & fertilize the ovum. enzymes & acrosome of sperm help it penetrate egg. the plasma membrane of the ovum undergoes numerous changes that make it impenetrable to other spermatozoa. The nuclei of the ovum & the nuclei within the sperm fuse, restoring the diploid chromosome number & creating the zygote (fertilized ovum). The zygote quickly undergoes a process known as cleavage this is a period of rapid cell division during which the cells themselves don't grow. During this the zygote cinttinues to travel though the oviducts. within a few days, the zygote develops into a solid mass of cells known as the morula. the cells of the morula continue to divide & form into a hollow ball of cells called the blastocyst, stage begins as the zygite reaches the uterus. rests against the endometrillining of the uterus & releases enzymes that dissolve a small depression into the uterine wall. the blastocyst implants itself in the depression

THE PLACENTA - consists of two layers of membranous sacs filled with fluid that surrounds the developing embryo. The inner most layer, is the amniotic sac filled with amniotic fluid. the second layer the allantois, is surrounded by the chorion, which attaches to the uterine lining. the umbilical cord contains blood vessels and a drainage structure from the urinary bladder of the fetus. The placenta functions and brings nutrients from the maternal circulation to the developing fetus. The mechanism of attachement between the placenta and the uterine wall varies in different species.

PREGNANCY & PARTURITION - The gestation period refers to the length of time required from fertilization to birth. is usually divided into trimesters (thirds), during first, the zygote (now called an embryo) is implanted & start development. During the second, the developing offspring is called fetus, and the anatomical structures take shape, third, dramatic growth just before birth. The process of giving birth is referred to as "parturition. Hormonal changes particularly decreases in the progesterone levels occur just before the onsrt of parturition. estrogen & prostaglandin levels rise & increase the sensivity of th myometrium to oxytocin which stimulates contraction of the myo & signals the beginning of labor. labor is divided into three stages, the initial stage involves uterine contractions that press the fetus against the cervix & cause the cefvical muscles to relax. the second stage involves rupture of the membranous scas covering the fetus & strong contractions of abdominal & uterine muscles that push the fetus through the vagina. the final stage of labor is the delivery of placenta, the placenta seperates from the wall of the uterus & is expelled by weak uterine contractions following parturition, the uterus slowly contracts & returns to its nonpregnant size. This process, known as involution, may take from a few weeks tp a few months

MAMMARY GLANDS & LACTATION - Mammary glands are a form of sweat glands modified to produce milk, vital to newborn animals, both male & female possess mammary glands. hormonal control causes these glands to produce milk. only female animals may produce hormones involved in milk production & release, the primary hormones involved are prolactin, FSH, & LH. teat means nipple. lactation is the process of producing milk & begins just before parturition. the first substance is not mlik, premilk called colostrum, is protein rich fluid that also contains electrolytes, lipids, & maternal antibodies

CHAPTER TWO SELF CHECK ON PAGE 42

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CHAPTER 3

THE URINARY SYSTEM - Has several functions including the following:

Disposing of the body's metabolic wastes

Helping to maintain the amount of water in the body

Controlling the pH level of the blood

Balancing the body's proportion of electrolytes

Eliminating certain drugs & hormones in the body

Assisting in the regulation of blood pressure

Urine is the final product of the urinary system. The composition of urine is determined by physiological needs as well as the state of the urinary system. The urinary system is comprised of two kidneys, two ureters. a urinary bladder, & a urethra. Kidneys produce urine that's carried to the bladder, which retains urine until urination occurs (micturition).

THE KIDNEYS - Each kidney lies in a space called a "retroperitoneal space," dorsal to, but separate from, the peritoneal (abdominal) cavity. The kidneys are lateral & very close to the spine & are caudal to (toward the back of) the liver. All kidneys have an indentation in the medial side, closest to the spine, called the "renal hilus," where the blood vessels enter & the ureter exits the kidney. The outer surface of the kidney is covered with a layer of tough connective tissue called the "capsule." The cortex is composed of small tufts of capillaries called "glomeruli" The outer coarse layer of renal tissue is called "cortext." The "medulla" is the kidney's inner core & contains many microscopic tubules arranged in a parallel manner. The arrangement gives the medulla a striped appearance. (most animals) The renal pelvis is a funnel-shaped space into which the tubules of the medulla empty urine. The pelvis empties into the ureter. cows don't have one. Kidney stones or "calculi" may form I the renal pelvis & prevent outflow of urine, creating distention of the kidney (hydronephrosis). The medulla is divided into wedges by projections of cortial tissue (renal columns). each kidney is supplied with blood by a renal artery which branches off the aorta.once inside the kidney the renal artery branches several times to form "interlobular arteries" that run between the wedges.

MICRISCOPIC ANATOMY OF THE KIDNEYS - The functional unit of the kidney is the "nephron," consists of a glomerulus & the associated bowman's capsule, renal tububles, & blood vessels (afferent & efferent arterioles as well as peritubular capillaries) thousands of nephrons act independently to form urine in kidney. A "glomerulus" is a globular tuft of capillaries supplied by a branch of an interlobular artey, an afferent arteriole. Blood leaves th glomerulu via the efferent arteriole. The efferent arterioles carries the blood to the peritubular capillaries. The glomerulus is surrounded on all sides by a thin layer of cells known as bowman's capsule. the renal medulla consists of only renal tubules, which generally run from the cortex &through the medulla to the renal pelvis. immediately after leaving bowman's capsule, the first part of the tubule is convoluted. therefore, it's called the "proximal convoluted tububle" before it straightens out to become the "descending loop of henie" at various depths within the kidneysthe tubule makes a U-turn & heads back toward the cortex as the ascending loop of nele. near the proximal convoluted tubule level, the tubule becomes convoluted again & is called the "distal convoluted tubule" its known as the convoluted ntubule before making another U-turn to head back toward the medulla as the collecting tubule. The bowman's capsule & the lining of the tubules are composed of a single layer of renal epithelial ells.. beneath these cells is a basement membrane that provides structural support for the tubular calls. on the other side of the basement membrane are the walls of the peritubular cappilaries that intermesh with the tubules. The :glomerulus functions as a filter to remove waste & some water from the blood. The result is the production of urine that enters the proximal convoluted tubule. As urine passes through the tubule its modified by the addition or removal of water, electrolytes, pH buffers & hormones or drugs.

THE FORMATION OF URINE - Urine is a liquid waste product composed primarily of water, in this water a variety of substances are dissolved, including by-products of metabolism, unneeded electrolytes, pH buffers, & ,miscellaneous substances such as drugs or hormones. The goal of the kidneys is to produce urine that balances the level of these substances in the body. Kdineys as a filter for blood, removing the unneeded & toxic substances & retaining the needed materials. Thus, the urinary system is essential to maintaining homeostasis (balance of the internal environment) The process of urine formation in the nephron occurs in two steps:

Filtration of blood by the glomerulus

Modification of the filtrate through reabsorption & secretion

The afferent arteriole carries blood from the renal artery to the glomerulus. Once in glomerulus blood pressure forces fluid & small molecules through the glomerular capillary wall, which is molre permeable than most capillary walls. glom is responsible for initial formation of urine. Larger substances & molecules,such as proteins,& blood cells are prevented from passing through the capillary bwall. the result is a liquid called the "glomerular filtrate" within the tubules, the filtrate is modified by two processes:

Reabsorption-substances are removed from the urine & returned to the blood

Secretion-substances are removed frim the blood & passed into the urine.

Two mechanisms exist for transporting substances across the tubule wall:

Active transport-requires energy

Passive transport-no energy is required

Substances is "creatinine" another waste product of metabolism. Substances that are either reabrobed nor secreted are useful for measurement of the glomerular filtration rate. The GFR is an approximation of renal blood flow & the ability of the kidneys to filter blood. cells in this part of the tubular system actively reabsorb materials from the filtrate, recovering about two-thirdsof the glomerular filtrate, recovering about two-thirds of glomerulus filtrate.

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SELF-CHECK 3

Renin- D = Hormone secreted by juxtaglomerular cells

Micturition- I= Void of urine

Ureter- H= tube carryingurine from the kidneys to the bladder

Calculi- F= Kidney stones

Aldosterone- B= Hormone secreted by adrenal glands

Nephron- G= Functional unit of the kidney

Erythropoietin- J= Hormone stimulating red blood cell production

Urethra- A= Tube carrying urine from the bladder to the external enviroment

Vasopressin- E= Antidiuretic hormone

Hydronephrosis- C= Distention of the kidney

The outer layer of renal tissue is called the CORTEX , whereas the inner layer of renal tissue is called the MEDULLA .

The four major components of the nephron are GLOMERULUS, BOWMAN'S CAPSULE, RENAL TUBULES, & RENAL BLOOD VESSELS.

Cattle & pigs have a SIGMOID FLEXURE, which is an S-shaped twist in the membranous urethra.

The four major components of the urinary system are KIDNEYS, URETERS, BLADDER, & URETHRA.

The type of cells lining the bladder wall mucosa are called TRANSITIONAL CELLS.

The kidneys of the horse are unique because the left & right kidneys differ in SHAPE.

The right kidney of the cow is on the LEFT side of the median plane.

In males, the urethra initially passes through the PROSTATE GLAND.

Renin acts on ANGIOTENSINOGEN, which changes it into ANGIOTENSIN.

The maintenance of balance of the internal environment of the body is called HOMEOSTATSIS.

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SELF-CHECK 2

1. The process that results in the formation of mature spermatozoa is SPERMATOGENESIS .

2. Cells that provide nutritional support to developing spermatozoa are called SERTOLI cells.

3. Spermatozoa are stored in the EPIDIDYMIS until ejaculation.

4. In canines, the urethra lies in a groove of bone known as the OS PENIS .

5. The primary hormone involved in initiation of the ovarian cycle is FOLLICLE-STIMULATING HORMONE (FSH) .

6. Species that have continuous ovarian cycles only at specific times of the year are called SEASONALLY POLYESTROUS .

7. The corpus luteum forms during the METESTRUS stage of the estrous cycle.

8. The process that activates the spermatozoa before fertilization is CAPACITATION .

9. The zygote develops into a hollow ball of cells called the BLASTOCYST .

10. The innermost sac surrounding the fetus is filled with AMNIOTIC FLUID .

11. The process of giving birth is called PARTURITION .

12. The hormone that stimulates contraction of structures in the female reproductive tract is OXYTOCIN .

13. A premilk substance secreted by mammary glands that contains proteins & maternal anti-bodies is COLOSTRUM .

14. The four structure in the female reproductive tract are the OVARIES, OVIDUCTS, UTERUS, & VAGINA.

15. The process of oogenesis produce one OVUM & three POLAR BODIES.

16. Fertilization normally occurs in the OVIDUCTS.

17. Cornification of vaginal epithelial cells involves a layer of KERATIN on the surface of the cells.

18. The drainage structure from the urinary bladder of the fetus is called the URACHUS.

19. List in order the four stages of the estrous cycle: PROESTRUS, ESTRUS, MELESTRUS, DIESTRUS

20. T or F? The female mammalian parent produces gametes that determine the baby sex? FALSE

Page 10

SELF-CHECK 1

Fermentation- F= Process of bacterial digestion of plant material

Pylorus- D= Muscular sphincter between the stomach & duodenum

Pulp- H= Sensitive core of the tooth

Serosa- B= Outer lining of the gastrointestinal system

Rumen- E= Largest compartment of a compound stomach; site of fermentation

Emulsification- G= Process of bacterial digestion of plant material

Esophagus- A= Muscular tube located between the pharynx & stomach

Incisors- J= Basic process of intestinal digestion

Hydrolysis- I= Basic process of intestinal digestion

Enamel- C= Inorganic calcified layer of the tooth

The small intestine is divided into three parts, namely, the: D= Jejunum, ileum, & duodenum

The four layers of the gastrointestinal wall, from inside to outside, are: B= Mucosa, submucosa, muscularis, & serosa.

In which area of the gastrointestinal tract does most digestion & absorption occur in a dog? B= Cecum

Which enzymes are secreted by the pancreas? C= Chymotrypsinogen, trypsinogen, lipase, & amylase.

The portal triad in the liver contains which three structures? A= Hepatic artery, portal vein, & bile duct

Digestive ENZYMES are proteins that help break down molecules of proteins, carbohydrates, & facts

What are four functions of the liver? BILE PRODUCTION, DETOXIFICATION, BACTERIA REMOVAL, PROTEIN PRODUCTION, GLYCOGEN STORAGE

Tall, thin cells lining the surface of the villi are ENTEROCYTES that are covered with finger-like projections called MICROVILLI .

Name the four layers of a tooth: PULP, DENTIN, ENAMEL, CEMENT.