Homeostasis questions

When the body maintains a dynamic equilibrium with small fluctuations e.g. blood pH, body temperature and concentration of urea

A small change in one direction is detected by sensory receptors and as a result the effectors work to reverse the change and restore conditions back to base levels. They essentially reverse the initial stimulus e.g. blood sugar levels and water balance

A change in the internal environment of the body is detected by sensory receptors and the effectors are stimulated to reinforce that change and increase the response e.g. blood clotting and release of oxytocin during childbirth.

1. Waste heat from respiration 2. Conduction from surroundings 2. Convection from surroundings 3. Radiation from surroundings

1. Evaporation of water 2. Conduction to surroundings 2. Convection to surroundings 3. Radiation to surroundings

They use their surroundings to warm their bodies. Their core body temperature relies heavily on the environment. e.g. invertebrates, fish, amphibians and reptiles.

Rely on metabolic processes to warm up and maintain a stable core body temperature, regardless of the temperature of the environment. They have increased metabolic needs compared to ectotherms.

1. Bask in the sun 2. Orientate their bodies so the maximum surface area is exposed to the sun. 3. Pressing their bodies against the warm ground (conduction)

1. Shelter from the sun by seeking shade. 2. Orientate their bodies so that the minimum surface area is exposed to the sun 3. Press their bodies against cool ground 4. Bathe in water 5. Minimise movements to reduce the metabolic heat generated

1. Dark colours absorb more radiation than light colours 2. Alter their heart rate to increase or decrease the metabolic rate

1. Internal exothermic metabolic activities (G) 2. Basking in the sun/ avoiding sun 3. Wallowing in water to cool down (L) 4. Digging burrows to keep cool (L) 5. Hibernation (L) 6. Clothes to stay warm. (G) 7. Houses are built and heated/cooled to maintain an ideal temperature. 8. Pressing themselves against warm/cool surfaces

1. Vasodilation 2. Increased sweating 3. Reducing the insulating effect of hair 4. Large surface area:volume ratio to maximise cooling 5. Pale fur to reflect radiation

The arterioles near the surface of the skin dilate. This forces blood through the capillary networks close to the surface of the skin where heat is lost through radiation and conduction, if pressed against a cool surface.

As the sweat evaporates from the surface of the skin, heat is lost, cooling the blood below the surface.

Avoids trapping an insulating layer of air.

1. Vasoconstriction 2. Shivering 3. The insulating effect of hair- Traps an insulating layer of air 4. Thick layer of insulating fat underneath the skin 4. Small surface area:volume ratio to minimise heat loss.

The blood flows through capillary networks away from the surface of the skin, which minimises heat loss through the surface of the skin .

Shivering increases the metabolic demands of our bodies and leads to an increase in respiration which produces heat as a waste product.

The removal of the waste products of metabolism from the body.

1. Carbon dioxide - Waste product of respiration. Excreted from the lungs 2. Bile - Formed from the breakdown of haemoglobin. Responsible for the colour of faeces. 3. Urea - Formed from the breakdown of excess amino acids by the liver. Excreted by the kidneys in the urine.

A reddish-brown organ involved in detoxification in our bodies. Made up of several lobes and has a very rich blood supply.

Oxygenated blood is supplied to the liver by the hepatic artery.

Blood is removed from the liver and returned to the heart via the hepatic vein.

Carries blood loaded with the products of digestion from the intestines to the liver and is the starting point for many metabolic reactions. Around 75% of the blood flowing through the liver comes from the hepatic portal vein.

Hepatocytes

1. Large nuclei 2. Prominent Golgi Apparatus 3. Lots of mitochondria, indicating they are very active cells

The site where the blood from the hepatic artery and the hepatic portal vein is mixed. This mixing increases the oxygen content of the blood from the hepatic portal vein.

Act as the resident macrophages of the liver, ingesting forgein paricles and helping to protect from disease.

The hepatocytes secrete bile from the breakdown of the blood into spaces called canaliculi, and from these the bile drains into the bile ductules, which take it to the gall bladder.

1. Carbohydrate metabolism 2. Deamination of excess amino acids 3. Detoxification

When blood glucose levels rise, insulin levels rise and stimulate hepatocytes to convert glucose into glycogen. They do the opposite under the influence of glucagon.

Hepatocytes carry out transamination which is the conversion of one amino acid into another. This is important because the diet doesn't always provide the required amino acids.

The removal of an amine group from a molecule.

1. The amine group is removed from the amino acid. 2. Then its converted to ammonia. 3. It is then combined with carbon dioxide to form urea. 4. Sent to the kidneys to be excreted.

1. Fed into cellular respiration. 2. Converted into lipids for storage

A set of enzyme controlled reactions that produces urea from ammonia produced by the amine group.

The liver is the site where toxins made in the body are detoxified and made harmless e.g. alcohol.

1. Hepatocytes contain the enzyme alcohol dehydrogenase which breaks down th ethanol into ethanal. 2. Ethanal is then converted into ethanoate, which is then used to build up fatty acids or used in cellular respiration.

A pair of reddish brown organs, surrounded by a thick, protective layer of fat and a layer of connective tissue. The kidney plays two important homeostatic roles in excretion and osmoregulation.

Renal arteries (branch of the abdominal aorta) and Renal veins which drains into the inferior vena cava.

Small structures that make up the kidneys. They act as filtering units.

Tubes that the urine passes out of the kidneys down. The urine is collected in the bladder.

When the bladdder starts to get full, the urine passes out of the body down the urethra.

1. Cortex - darker outer layer 2. Medulla - lighter area 3. Pelvis

Where the filtering of the blood takes place and it has a very dense capillary network carrying the blood from the renal artery to the nephrons.

Contains the tubules of the nephrons that form the pyramids of the kidney and the collecting duct.

The central chamber where the urine collects before passing out down the ureter.

1. Bowman’s capsule <br> 2. Proximal convoluted tubule (PCT) <br> 3. Loop of Henle <br> 4. Distal Convoluted tubule (DCT) <br> 5. Collecting duct <br>

A cup-shaped structure that contains the glomerulus

A tangle of capillaries. More blood goes into the glomerulus than leaves, due to the ultrafiltration that takes place.

The first coiled region of the tubule after the bowman’s capsule, found in the cortex of the kidney. This is where many of the substances needed by the body are reabsorbed into the blood.

A long loop of tubule that creates a region with a very high solute concentration in the tissue fluid deep in the kidney medulla. The descending loop runs down the cortex through the medulla to a hairpin bend at the bottom of the loop. The ascending limb travels back up through the medulla to the cortex.

" A second twisted tubule where the fine-tuning of the water balance of the body takes place. The permeability of the walls to water varies in response to the levels of ADH in the blood. Further regulation of the ion balance and pH of the blood also takes place in this tubule. "

" The urine passes down the collecting tube through the medulla to the pelvis. More fine-tuning of the water balance takes place – the walls of this part of the tubule are also sensitive to ADH. "

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" Ultrafiltration in the kidney tubules is a specialised form of the process that results in the formation of tissue fluid in the capillary beds of the body and is the result of the structure of the glomerulus and the cells lining the bowman’s capsule. </p> "

" A wide afferent (incoming) arteriole from the renal artery. The blood leaves through a narrower efferent (outward) arteriole and as a result there is considerable pressure in the capillaries of the glomerulus. This forces the blood out through a capillary wall – acts as a sieve "

" Made up of a network of collagen fibres and other proteins that makes and acts a second sieve. Most of the plasma contents can pass though the basement membrane but blood cells and proteins are retained in the capillary because they are too big to fit. </p> "

" Act as an additional filter. They have extensions called pedicels that wrap around the capillaries, forming slits that make sure any cells, platelets or large plasma proteins that have managed to get through the epithelial cells and the basement membrane don’t get through into the tubule itself. </p> "

Because it is less concentrated than the blood plasma

All of the glucose, amino acids, vitamins and hormones are moved from the filterate back into the blood by active transport.

" 1. They are covered with microvilli, greatly increasing the surface area over which substances can be absorbed. 2. They have many mitochondria provide the ATP needed in active transport systems. "

They diffuse into the extensive capillary network which surrounds the tubule down steep concentration gradients. The filtrate reaching the loop of Henle at the end of the PCT is isotonic with the tissue fluid (same concentration) surrounding the tubule and the blood.

Enables mammals to produce urine more concentrated than their own blood. Different areas of the loop have different permeabilities to water.

Leads from the PCT – water moves out of the filtrate down a concentration gradient. The upper part is impermeable to water, but the lower part of the descending limb is permeable to water.

The filtrate is isotonic with the blood. As it travels down the limb, water passes out of the loop into the tissue fluid by osmosis down a concentration gradient. It then moves down another concentration gradient into the blood.

Very permeable to sodium and chloride ions and they move out of the concentrated solution by diffusion down a concentration gradient..

Sodium and chloride ions are actively pumped out into the medulla tissue fluid against a concentration gradient. This produces very high sodium and chloride ion concentrations in the tissue fluid.

The ascending limb of the loop of Henle is impermeable to water, so water cannot follow the ions down a concentration gradient, causing the fluid left in the limb to become increasingly dilute.

Balancing the water needs of the body takes place. These are also the areas where the permeability of the walls of the tubules varies with the levels of ADH.

Have many mitochondria, so they are adapted to carry out active transport. It also plays a role in balancing the pH of the blood.

The main site where the concentration and volume of the urine produced is determined.

Water moves out of the collecting duct by diffusion down a concentration gradient as it passes through the renal medulla and the urine becomes more concentrated. The permeability of the collecting duct to water is controlled by the level of ADH, which determines how much or little water is reabsorbed.

Controlling the water potential of the blood within narrow boundaries, regardless of the activities of the body e.g. eating a salty meal, drinking lots of water or visiting a hot climate.

1. Drinking water 2. Food 3. Respiration in cells

1. Urine 2. Sweat 3. Exhaled air 4. Faeces.

ADH increases the permeability of the DCT and the collecting duct to water.

It binds to the receptors on the cell membrane of the collecting ducts and triggers the formation of cAMP, which causes a cascade of events.

" 1.Vesicles in the cells lining the collecting duct fuse with the cell surface membrane on the side of the cell in contact with the tissue fluid of the medulla. 2. The membranes of these vesicles contain aquaporins and when they are inserted into the cell surface membrane, they make it permeable to water. 3. This provides a route for water to move out of the tubule cells into the tissue fluid of the medulla and the blood capillaries by osmosis. "

Protein-based water channels

Levels of cAMP fall, then the water channels are removed from the tubule cell membranes and enclosed in vesicles again. The collecting duct becomes impermeable to water again, so no water can leave.

The production of large amounts of dilute urine and maintains the water potential of the blood and the tissue fluid.

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The permeability of the collecting duct is controlled to match the water requirements of the body.

1. Water 2. Urea 3. Mineral salts

A well known symptom of diabetes

Suggests muscle damage

Drugs or metabolites (breakdown products of drugs) are filtered through the kidneys and stored in the bladder, it is possible to find drug traces in the urine some time after a drug has been used.

1..Kidney infections, where the structure of the podocytes and the tubules themselves may be damaged or destroyed 2. Raised blood pressure that can damage the structure of the epithelial cells and basement membrane of the Bowman’s capsule 3. Genetic conditions

1. Proteins in the urine – if the basement membrane or podocytes of the Bowman’s capsule are damaged, they no longer act as filters and large plasma proteins can pass into the filtrate and are passed out in the urine. 2. Blood in the urine – another symptom that the filtering process is not working.

" The concentrations of urea and mineral ions build up in the body. The effects include: 1. Loss of electrolyte balance – if the kidneys fail, the body cannot excrete excess Na, K and Cl ions. This causes osmotic imbalances in the tissues and eventual death. 2. Build-up of toxic urea in the blood – if the kidneys fail, the body cannot get rid of urea and it can poison the cells. 3. High blood pressure – the kidneys maintains the water balance of the blood. If they fail, blood pressure increases, and causes a range of health problems including heart problems and strokes. 4. Weakened bones as the calcium/phosphorus balance in the blood is lost. 5. Pain and stiffness in joints as abnormal proteins build up in the blood. "

The rate at which blood is filtered in the Bowman’s capsule of the nephrons

Used as a measure to indicate kidney disease. A blood test measures the level of creatine in the blood. Creatine is a breakdown product of muscles and is used to give an estimate GFR.

Age and gender need to be considered as GFR decreases with age and is higher for men than women because men usually have more muscle mass.

Doesn't fall below 70

Below 60 for more than 3 months.

Below 15, the kidneys are filtering so little blood they are virtually ineffective.

1. Renal dialysis 2. Transplant

The function of the kidneys is carried out artificially.

Replaces the functions of the failed kidneys.