Biology chapter 15 homeostasis and excretion

the body maintains a dynamic equilibrium with small fluctuations over a narrow range of conditions

Definition of homeostasis?

negative feedback systems work to reverse the initial stimulus

example: control of blood sugar with insulin and glucagon

what is negative feedback?

one example of a system in the body?

when a change is detected in the body, the effectors work to reinforce the change and increase the response

example: during childbirth, head presses against cervix which stimulates oxytocin and causes contractions which further pushes baby against cervix

what is positive feedback

one example

use surroundings to warm their bodies. core body temp is reliant on environment

fish, amphibians and reptiles

those living water don’t have problems as water has a high heat capacity and temp remains constantw

what is an ectotherm?

mammals and birds

rely on metabolic processes to warm up and maintain a stable core temp

What is an endotherm?

• behavioural responses like going in the sun or shade, press body on warm ground through conduction.

• some physiological responses such as being dark to absorb more heat

• need less food and can survive in harsher habitats

how do ectotherms regulate temperatures?

• receptors in the skin

• receptors in hypothalamus

how do ectotherms detect temp changes?

• vasodilation of blood vessels to force blood closer to the skin so heat can escape

• increased sweating, when sweat evaporates from the skin, heat is taken with it and cools the blood

• hairs lie flat on the skin to stop insulating

• high SA:V ratio to maximise cooling

cooling mechanisms of endotherms?

• shivering - the metabolic heat from contracting muscles heats up the body

• some animals have small SA:V ratio or fat stores

• vasoconstriction

• hairs rise up to insulate

• decreased sweating

warming mechanisms of endotherms?

the removal of waste products of the metabolism found in the body

CO2, bile bigments (billirubin) and urea from breakdonw of amino acids

excretion defintion

what do mammals excrete?

brings oxygenated blood to drive the metabolic reactions in liver

what does the hepatic artery bring to the liver?

brings blood straight from gut and is rich in glucose, amino acids

what does the hepatic portal vein bring?

called hepatocytes

• large nuclei

• prominent Golgi apparatus

• Lots of mitochondria as they are metabolically active

features of the liver cells and what are they called?

• blood from hepatic artery and portal vein is mixed in sinusoids surrounded by hepatocytes

• mixing increases oxygen content of the blood from the hepatic portal vein

• sinusoids have Kupffer cells which are like macrophages and ingest foreign particles

• hepatocytes secrete bile into the bile canaliculi which drains into bile ductules

label parts of the liver lobule

• control blood glucose, amino acid and lipid levels

• glycogen is stored in the hepatocytes

• Synthesis of plasma proteins, cholesterol, RBC in foetus

• detoxification of alcohol

• Breakdown of hormones

• Synthesis of urea from amino acids (deamination)

• Convert one maino acid into one that is neccessary

functions of liver and hepatocytes

ornithine cycle

• ammonia is produced from deamination of amino acids

• in the ornithine cycle ammonia converted to urea and useful products

• water, urea and CO2 made

what is the cycle that creates urea?

• breakdown of hydrogen peroxide

• hepatocytes have catalse, splits hydrogen peroxide into oxygen and water

• alcohol dehydrogenase which breaks ethanol to ethanal

detoxification

• cortex - dark outer layer where filtering of blood happens

• medulla - lighter inner section which has tubules of the nephorns

• the pelvis - central chamber where urine collects

kidney structure?

• bowman’s capsule - has glomerulsu which is a tangle of capillaries

• proximal convulated tubule - many substances are reabsorbed here

• loop of henle - long loop that has high solute conc

• distal convoluted tubule - fine tuning of water balance in blood, ions and pH

• collecting duct - sensitive to ADH

structure of the nephron label

what happens in each part of nephron?

glomerulus and bowman’s capsule

1. the glomerulus is supplied with blood from the afferent arteriole and leaves through narrower efferent arteriole

2. high hydrostatic pressure forces blood through capillary wall, through basement membrane and pediciles of the podocytes

3. proteins and many blood cells are retained as they are too big

4. filtrate then eneters the capsule and has glucose, salt, urea.

ultrafiltration

where does it happen?

process?

proximal convoluted tubule:

• all of the glucose, amino acids, vitamins and hormones are reabsorbed back into the blood by active transport

• the cells are adapted by:

  • covered with microvili which increases the surface area

  • many mitochondria to make ATP for active transport

• once they are removed, they diffuse into capillary network

• the filtrate reaching the loop of henle is isotonic with tissue fluid. 80% of filtrate has been reabsorbed

selective reabsorption

where does it happen and process?

• Na+/K+ pump uses ATP and pumps Na+ ions into the blood from PCT cells

• This means there is a low conc of Na+ in the PCT so by a cotransport protein, Na+ and glucose are reabsorbed into PCT cells

• Glucose can then diffuse into the capillaries down their conc gradient

• water follows by osmosis

how are glucose and amino acids actively reabsorbed in PCT?

• called the countercurrent multiplier system

• The ascending limb actively pumps out sodium and chloride ions into the medulla to reduce the water potential of the medulla

• The ascending limb is impermeable to water

• Water then leaves the descending limb by osmosis due to the low water potential in the medulla.

• The fluid at the bottom of the loop of Henle is very concentrated, so when it starts moving up the ascending limb, ions can passively move down conc gradient into the medulla

• Desert animals have longer loops of Henle to reabsorb more water

What happens in the loop of henle?

• permeability varies with ADH

• cells are adapted to carry out active transport

• if body lacks salt, sodium ions will be pumped out and Cl- will follow due to gradient

• water can also leave and make the urine more concentrated

what happens in the DCT?

• water moves out by diffusion down a concentration gradient so urine is more concentrated

• the level of sodium ions in the surrounding tissue fluid increases through medulla so more water can be reabsorbed

• permeability is controlled by ADH

• ADH made by the hypothalamus and secreted by the pituitary

• ADH increases permeability

what happens in the collecting duct?

• released from pituitary and doesn’t cross cell

• binds to receptors and triggers formation of cAMP as a second messenger

• vesicles in collecting duct cells fuse wth cell surface membrane

• they have aquaporins which make CD permeable to water

mechanisms of ADH action

• in hypothalamus

• when too less water, water potential drops so nerve impulses are sent to posterior pituitary to release ADH

• when too much water ADH release is inhibited

where are osmoreceptors located and how to they work?

• mobile monoclonal antibodies made to be complementary to hCG are attached to a small coloured bead

• hCG in urine binds to mobile antibodies and form hCG/antibody complex

• immobilised monoclonal antibodies arranged in a line and only bind to hCG/antibody complex

• another line of immobilised monoclonal antibodies bind to mobile antibodies whether hCG is present or not, to show if the mobile antibodies are moving up the stick

how do modern pregnancy tests work?

drugs that mimic the action of testosterone and stimulate muscle growth

can be detected by gas chromatography of the urine

what are anabolic steroids?

• damage to basement membrane or podocytes

• cysts

• damage to structure of epithelial cells

causes of kidney failure?

• protein in urine due to Bowman’s capsule damage

• Blood in urine

• high blooc pressure

• build up of toxic urea in the blood

measured by measuring glomerular filtration rate (cm³/min)

effects of kidney failure?

Haemodialysis:

• blood leaves body through artery into the machine

• flows between partially permeable dialysis membranes

• mimic the basement membrane

• urea moves out down the concentration due to dialysis fluid which has no urea

• but has same plasma and glucose levels as blood

Transplant:

• risk of rejection

• better for patient if it works, as dialysis takes too long

• Immunosuppressant drugs can be harmful

treatments to kidney failure?
how does each of the methods work and pros and cons?