D3.3 homeostasis (year 6) Flashcards
h
Examples of parameters controlled by homeostasis
- internal body pressure
- blood pH
- blood glucose conc
- blood osmotic conc
Why is negative feedback used in homeostasis over postive feedback?
Negative feedback returns homeostatic variables to a set point from values above or below the set point, keeping a value within a set range
whereas positive feedback (e.g. contractions during labour when giving birth) amplifies a response
Examples of hormones involved in homeostasis
Insulin, glucagon:
Insulin: produced by beta cells in pancreas, opens protein channels in cell plasma membranes to allow glucose to diffuse into cell.
Also stimulates muscle and liver cells to take in glucose and convert it to glycogen, to lower blood insulin levels
Glucagon: alpha cells of pancreas produce glucagon, stimulating the hydrolysis of glycogen in liver and muscle cells. Hydrolysis of glycogen produces glucose, increasing glucose conc.
Describe the physiological changes, risk factors, methods of treatment of type I/II diabetes
Type I:
- an autoimmune disease that causes the immune system to destroy the beta cells of the pancreas
- controlled diet, insulin injections needed
- risk factors include family history and age
- no prevention
Type II:
- body cell receptors do not respond properly to insulin and so do not intake enough glucose (insulin resistance)
- risk factors include family history, obesity, lack of exercise.
- prevented by healthy diet and lifestyle
- insulin injections to not work
SIDE EFFECTS OF BOTH TYPES:
- damage to eye retina = blindness
- kidney failure
- nerve damage
- poor wound healing
- increased risk of cardiovascular disease
Diff btwn ectothermic/endothermic animals
Ectothermic:
- internal temp equalizes w. the environment (cold-blooded)
- do not have to metabolise foods to generate body heat = eat less
Endothermic:
- maintain a steady internal temp that is always higher than environment
- requires extra nutrition to generate body heat
Describe both ways humans thermoregulate body temp
Body temp above 37:
- Hypothalamus uses receptors to sense blood temp + skin peripheral receptors send impulses to hypothalamus
- hypothalamus sends impulses to arterioles near skin to induce vasodilation = more blood travelling through capillaries = more heat released into the surrounding environment
- hypothalamus also initiates perspiration = evaporation of sweat provides evaporative cooling as heat from body is transferred to sweat, initiating the phase change of evaporation
Body temp below 37:
- Hypothalamus uses receptors to sense blood temp + skin peripheral receptors send impulses to hypothalamus
- hypothalamus sends impulses to arterioles to induce vasoconstriction = less blood travelling through capillaries = more blood shunted to internal organs = less heat released into the environement
- vital organs receive more blood
- Epinephrine is released = goosebumps and raised hairs = insulating layer of air
- When peripheral thermoceptors sense cold, pituitary gland is stimulated to release hormones that activate the THYROID gland to release THYROXINE = increase metabolic rate of all body cells to generate heat
- Shivering is an autonmic response by the hypothalamus to generate body heat
- there are other concious responses by the cerebrum e.g. moving around, seeking shade etc
- some animals have blubber that is adipose tissue to retain warmth generated by metabolic activities
How do newborns generate enough body heat?
Newborns have a higher proportion of fat called brown adipose tissue which contains more mitochondria than other fat cells.
When needed, the mitochondria begins a type of cell respiration called UNCOULPED RESPIRATION which does not produce ATP as glucose is oxidised for the sole purpose of generating enough body heat.
Differences btwn osmoregulation and excretion
Osmoregulation:
- the regulation of osmotic conc., where the water content of urine is based on water intake, perspiration levels etc.
Excretion:
- filtering many solutes out of blood and using cellular transport mechanisms to regulate what stays in urine and what returns to blood.
Practice drawing/labelling a kidney
There should be:
- glomerulus (filter various substances from blood)
- bowmans capsule (surrounding glomerulus
- proximal convoluted tubule, loop of henle, distal convoluted tubule (extends from the bowmans capsule)
- peritubular capillary bed (surrounds the 3-part tubule)
- collecting ducts
Describe the role of glomerulus, bowmans capsule, PCT in excretion
glomerulus:
- unfiltered blood enters through the afferent arteriole, passes through the glomerulus, exits via the efferent arteriole
- the efferent arteriole has a smaller diameter than the afferent arteriole to create a pressure differential to drain the blood from glomerulus.
- Glomerulus is made of capillaries with fenestrations (small slits) that open under high pressure.
Bowmans capsule:
- ultrafiltration: various substances are filtered through the glomerulus under high blood pressure which pass through the fenestrations and the basement membrane (of the bowmans capsule). This prevents larger molecules such as proteins from being part of the filtrate.
- the filtrate eventually becomes urine and enters the PCT.
- The rest of the blood exits by the efferent arteriole
Proximal convoluted tubule:
- the wall is 1 cell thick, with the inner portion of the lumen having microvilli to increase SA:V for reabsorption
- As the urine still contains some substances that the body cannot afford to lose (e.g. mineral ions) + the body a great deal of water, reabsorption occurs in the PCT and are taken back into the bloodstream by the peritubular capillary bed
Role of loop of henle
to MAINTAIN HIGH OSMOTIC CONC IN THE MEDULLA to FACILITATE WATER REABSORB in the collecting ducts
- the descending portion of the loop of Henle is permeable to water and impermeable to Na+ ions
- the ascending portion is impermeable to water and permeable to Na+ ions
- As the filtrate moves up, Na+ ions are actively transported out and enter the fluid surrounding the loop of Henle
Describe how osmoregulation in collecting duct is regulated
- The collecting duct is differentialy permeable to water, which is controlled by AntiDuretic Hormone (ADH)
- ADH is secreted from the pituitary gland and its secretion is controlled by the hypothalamus
Osmoregulators in hypothalamus sense water needs to be retained > more ADH is secreted > collecting duct becomes more permeable to water > water moves by osmosis out of collecting duct to medullary intestinal fluid > water enters the peritubular intestinal fluid and returns to the bloodstream.
Describe the effect of ADH on aquaporins in collecting duct cells
Aquaporins allow polar water molecules to move through the cell membrane
- When ADH is present, aquaporin vesicles merge with the plasma membrane, leaving the aquaporins inserted into the membrane
- water can now move by osmosis through the aquaporins to the other side of the cell
- When ADH conc decreases, the plasma membrane INVAGINATES and stores the aquaporins in intracellular vesicles once again. Water can now only remain in the collecting duct to be removed by urine
Describe + examples of changes in blood supply to organs in the body
Vasodilation and vasoconstriction of arterioles control blood supply. Greater blood supply = vasodilation, vice versa. When vasodilation/vasoconstriction occurs, vasoconstriction/vasodilation must take place in the other arterioles of the body to maintain blood pressure.
Examples:
- kidneys receive maximum blood flow when resting/sleeping
- blood flow to brain is maximum during deep sleep (REM)
- Skeletal muscles + digestive system have the largest blood volume changes
- the brain and kidneys can only tolerate small changes in blood supply
