Mind map

The Kidney & Homeostasis

Shehzeb B Component 3 English

Map content

Structure
- Cortex
  - Bowman's capsule
    - Proximal convoluted tubule - mitochondria and brush border
      - Distal convoluted tube- no brush border
        Collecting duct
- Medulla
  - Loop of Henle
    - Collecting Duct
    - Increases solute conc of the medulla
      - So water is reabsorbed from the DCT & collecting duct
        2 Main Sections
        Ascending Loop of Henle
        Impermeable to water
        Na & Cl pumped out via active transport
        Lowers W.P in medulla
        Descending Loop of Henle
        Permeable to water
        Water moves out by osmosis
        Into tissue fluid that goes into the vasa recta
        Salt conc is higher in descending limb
        Fluid becomes saltier as it goes down the descending loop
        Hence lower W.P
        As fluid ascends the W.P increases
        Because Na & Cl move out
    - Acts as Hair Pin Counter Current Multiplier
      - Because blood & filtrate flow in opposite directions
        As flow of fluids (where exchange takes place) is in opp directions
    - Adaptations
      - Dry environments
        Need to save water so there is a long loop
        Leads to higher salt conc = more water reabsorbed
      - Wet environments
        No need to save water so small loop
- Vasa recta: A capillary network surrounding the Loop of Henle
1) Ultrafilteration
- When a high pressure is used to filter a substance
  - High pressure is generated by
    - Afferent arteriole having a wider diameter than the Efferent arteriole
    - The high pressure forces small molecules (Mr < 68000) through
      - 1) Fenestrations
        Pores in the capillaries' epithelial cells
      - 2) Basement membrane
        Extrinsic proteins: Mainly collagen & glycoproteins
      - 3) Podocyte (cell) slits
        Consist of gaps in pedicals
      - The liquid formed is called glomerular filterate
        Solutes include: Urea, Glucose, Salts, Water, Amino acids
2) Selective Reabsorption
- Occurs in the proximal convoluted tubule (PCT)
  - Adapted well due to its length & surface area
    - PCT cells are specialised by having:
      - Cuboidal epithelial cells w/Microvilli - Increases the SA - makes a brush border
        Cell membrane has specific protein carriers
        Mitochondria- For ATP- Active transport
        Tight junctions to prevent leakage back into filtrate
        Close to the capillary network
  - Substances absorbed
    - Glucose by active/ co transport
    - Na+ & Cl- via active transport
    - Filtered proteins, some urea by diffusion
    - Water by osmosis
      - As water is reabsorbed the W.P drops
        By the end of the PCT the solution is isotonic
3) Osmoregualation
- DCT, Collecting Duct, Pituitary gland & Hypothalamus determine water lost
  - Detector: Osmoreceptors in hypothalamus
    - Co-ordinator: Posterior Pituitary gland
      - Effector: DCT & Collecting ducts
  - ADH increases permeability of DCT & collecting ducts
    - Making more concentrated urine w/low vol
      - W.P = More negative = Osmoreceptors =
        More ADH made by posterior pituitary =
        ADH attaches to receptors on collecting duct increasing permeability
        By inserting Aquaporins (Water channels) = More water reabsorbed = Less urine
        ADH binds to membrane receptors
        Adenyl cyclase catalyses production of cyclic AMP
        Vesicles containing aquaporins move in & fuse w/membrane
        Making the water channels
        When intracellular Cyclic AMP levels fall
        Aquaporins are removed from membrane
        & they accumulate back in the vesicles
- Blood W.P can drop due to:
  - Sweating, reduced water intake, intake of salts
Functions
- Excretion: Removes nitrogenous metabolic waste from the body (urea)
  - Excess amino acids are deaminated making urea
    - Deamination
    - Transamination
      - Enzyme-catalysed reaction that transfers an amino group to an alpha-keto acid, making an amino acid
- Osmoregulation: Control water/solute conc
Kidney Failure
- Causes
  - Diabetes
  - High B.P
  - Auto-immune disease
  - Infection
  - Injury in an accident
- Treatment
  - Reducing protein intake
    - Lower urea production
  - Drug treatment
    - ACE inhibitors (block angiotensin; vessel constricting hormone)
    - ARBs: Angiotensin receptor blockers
    - Ca2+ Blockers: dilate blood vessels & reduce B.P
    - Beta blockers: Reduces effect of adrenaline (hormone increases heart rate & B.P)
  - Dialysis
    - Haemodialysis
      - Blood is taken from artery
        Passes through selectively permeable dialysis tubes
        Pores let small molecules pass through
        Blood & fluid use counter current mechanism
        Maximising diffusion
        Heparin is added to thin blood & stop it clotting
    - CAPD (continuous ambulatory peritoneal dialysis)
      - Thin membrane surrounds organs in abdomen (peritoneum)
        Dialysis fluid is added to peritoneal cavity
        Waste diffuses into fluid over 4 hours
        Happens 4 times a day
        This can allow someone to live their life
    - Problems w/dialysis
      - Erythropoietin production reduces
        Can lead to anaemia
      - Vitamin D isn't converted
  - Kidney transplant
    - Offered to patients w/end stage renal failure
Homeostasis
- The maintenance of a constant internal environment
  - I.e. In a dynamic equalibrium
- Factors include
  - Blood Glucose level
  - Body temp
  - Solute potential
- Negative feedback is mechanism that retains the norm
  - A change to the normal level initiates a response which reduces the effect/reverses/acts against the change
    - Components of mechanism
      - 1) Set point: Normal value for the body
        2) Receptor: Compares actual level w/the set point & signals the effector
        3) Co-ordinator: Informed by receptor of a change in the norm, sends info to effector
        4) Effector (muscle/gland): A process that is carried out to return levels to set point
- Positive feedback mechanism
  - In which an effector increases a change
    - Contraction in labour due to oxytocin
Metabolic water
- Water produced from the oxidation of food reserves
  - Xerocoles (Desert animals) rely completely rely on metabolic water
Types of nephrons
- Cortical nephron
  - Glomerulus in outer cortex
    - Short loop of henle, barely penetrates medulla
      - Found in humans, beavers etc & make dilute urine
- Juxtamedullary nephron
  - Bowman's capsule is closer to the medulla boundary
    - Long loop of henle goes deep into medulla
      - Desert animals have juxtamedullary nephrons
        Allow for maximal reabsorbption