Communication, Homeostasis and Energy

Page 1

Lesson 1 CTA - 09/06/2015

Stimulus -> Change in environment detected by organism that causes a response E.g temperature and light intensity.

Response -> Change in behaviour or physiology of organism in response to a stimulus.

Cells are not exposed to the external environment- their environment is the tissue fluid they are bathed in. Responses are triggered by changes in the fluid, regulated by blood.

The basic process of signalling- Signal molecules have complementary receptors on their specific target cells.

A good communication system:

Covers the whole body/organism

Enables cells to communicate with each other

Enables specific communication

Enables rapid communication

Enables both short and long term responses to occur

The two communication systems:

Neuronal- An interconnected network of neurones with signals diffusing across synapses. This system conducts signals quickly enabling rapid (e.g. reflex) responses.

Hormonal- Uses the blood stream to transport signals released by endocrine system cells. The hormones travel through the whole body but are only recognised by specific target cells. This system conducts longer term responses e.g. puberty.

Homeostasis- The maintenance of a constant internal environment despite changes in the environment.

Homeostasis can occur by two mechanisms- positive and negative feedback. Positive feedback is where any change in a parameter brings about an increase in that change. Negative feedback involves a change in parameter bringing about the reversal of that change to keep the parameter fairly constant.

The Communication Process: Stimulus -> Receptor (monitor conditions)-> Communication Pathway (may (not) pass through coordination centre such as brain) -> Effector -> Response

Lesson 1 SRI - 18/06/2015

Nervous System: Job- to detect changes in environment and allow body to respond. Consists of- Mainly the brain, spinal cord, nerve cells (neurones) and receptors.

CNS - brain and spinal cord PERIPHERAL- nerves in limbs, across thorax and abdomen.

Reflex Arc (involuntary): Stimulus -> Receptor activated -> Activation of sensory neurone -> (Relay in the CNS-signal sent to brain) -> Activation of motor neurone -> Response by effector

Receptors & Energy changes

Light sensitive cells in retina LIGHT -> ELECTRICAL

Olfactory cells in nose CHEMICAL -> ELECTRICAL

Taste buds in tongue, hard plate, epiglottis and oesophagus CHEMICAL -> ELECTRICAL

Sound receptors in inner ear KINETIC/SOUND -> ELECTRICAL

Muscle spindles ELASTIC POTENTIAL -> ELECTRICAL

Pressure receptors in the skin KINETIC -> ELECTRICAL

Key features of Neurones:

Long (transmit over large distances)

Gated ion channels in membrane controlling Na+, K+ and Ca2+

Na+/K+ pumps for active transport

Myelin Sheath insulates to prevent interference

Gaps between Schwann cells

Resting potential- K+/Na+ pumps more sodium out than potassium in (ratio 3:2). The inside of the cell becomes negative compared to the outside (-60mV) and the membrane is POLARISED.

Lesson 2 CTA - 23/06/15

Endocrine gland- gland that secretes hormones directly into the blood, no ducts

Exocrine gland- gland that secretes molecules directly into a duct

Hormone- Released into the blood to act as chemical messenger

Target tissue- A group of cells that have receptors embedded in the plasma membrane that are complementary to the specific hormone.

The cortex of the adrenal gland uses cholesterol to produce steroid hormones. The medulla (in the centre) is where adrenalin is manufactured; most cells have adrenalin sensors to prepare the body for activity.

Adrenalin:

relaxes smooth muscle in bronchioles

increases both stroke vol and heart rate

causes vasoconstriction (increases blood pressure)

converts glycogen to glucose

dilates pupils

increases mental awareness

inhibits the action of the gut

causes body hair to erect

Different hormones interact with target cells in different ways. Steroid hormones can enter cells and have a direct effect on activities in the nucleus. Protein hormones reply on a receptor in the membrane of target cells.

There are 4 main components in the protein hormone system: the hormone receptor, G protein (activated by hormone receptor complex, activates A.C), Adenyl cyclase (enzyme inside cell membrane that changes ATP to cAMP), and cAMP (2nd messenger, builds up in cytoplasm and activates enzymes like kinase).

Lesson 3 CTA - 29/06/15

The majority of pancreas function is enzyme manufacture (for digestion). Enzymes are secreted into the pancreatic duct and carried to the small intestine along with sodium hydrocarbonate for the neutralisation of chyme.

Islets of Langerhans- The islets have 2 types of cells; alpha cells manufacture and secrete glucagon to increase blood glucose concentration and beta cells manufacture and secrete insulin to lower blood sugar concentration. Both hormones are secreted directly into the blood. Both cells can monitor blood glucose and react (negative feedback) if the levels are changed from 90mg/100cm3 / 4-6mmol/dm3.

Most cells in the pancreas secrete digestive enzymes into tiny tubules. The tubules join and empty into the pancreatic duct carrying: amylase, trypsinogen (an inactive protease) and lipase.

Insulin-

Target cells: Liver cells (hepatocytes) and muscle cells

Binds to: receptors to cause G protein activation etc.

Effects: More glucose channels in cell membrane, more glucose enters cells, glycogenesis, glucose converted to fats, more respiration, lower blood glucose concentration.

Glucagon-

Target cells: Liver cells (hepatocytes)

Effects: Glycogenolysis, more fatty acids respired, glucose produced by gluconeogenesis, blood glucose concentration rises.