Topic 9.3 Homeostasis Flashcards
(Heart) Responding to demand
When the body demands more glucose and oxygen, the heart can respond in two ways:
-The stroke volume can be increased by a more efficient contraction of the ventricles.
-The heart rate can increase.
–> Athletes have a lower resting heart rate as the cardiac volume increases as it becomes clear from changes in the body that exercise is going to continue.
Nervous control of the heart
–> The cardiac control centre is situated in the medulla oblongata.
-Chemical, stretch and pressure receptors send nerve impulses to the cardiac centre.
-The cardiac centre responds by sending impulses to the heart along parasympathetic and sympathetic nerves.
–> Nerve impulses travelling down the sympathetic nerve releases noradrenaline to stimulate the SAN (which makes the heart beat more quickly).
–> In contrast, nerve impulses in the corresponding parasympathetic nerve release acetylcholine, inhibiting the SAN and slowing the heart down.
The role of baroreceptors
-Baroreceptors (found in sinuses of carotid arteries) are important in the feedback control of the heart rate during exercise.
-At rest, they send signals back through sensory neurones to cardiac centre of the brain.
-When exercise starts, the blood vessels dilate in response to adrenaline, and the blood pressure falls.
-When exercise is stopped, blood pressure in the arteries increases, so baroreceptors are stretched.
The role of chemoreceptors in the aorta
-Sensitive to the levels of carbon dioxide in the blood.
-As CO2 levels rise, pH of the blood goes down which is detected by chemoreceptors.
-They send impulses to the cardiac control centre in the medulla, and heart rate increases- giving increased blood flow to the lungs and more CO2 removed.
-pH then rises again.
-Chemoreceptors respond by reducing the number of impulses to cardiac centre, reducing the acceleration of the heart.
Hormonal control of the heart
-When you are stressed, the sympathetic nerve stimulates the adrenal medulla to release adrenaline.
-This binds to receptors in the target organ, including the SAN.
-This stimulates the cardiac centre in the brain, increases the impulses in the sympathetic neurones supplying the heart.
-This increases the heart rate supplying extra oxygen and glucose for the muscles and brain (for fight or flight).
Additional responses
-When many impulses travel along the sympathetic nerve to the heart to speed up, fewer impulses are sent along sympathetic nerves to many blood vessels.
-Causing the vessels to contract, narrowing the vessels.
-This way blood flow is diverted from temporarily less important areas to provide more blood for the heart and muscles to use.
Osmoregulation
Is the maintenance of the osmotic potential in the tissue of living organisms.
Both kidneys and the liver are involved in homeostatic control.
1) The liver breaks down excess amino acids and removes toxins from the blood.
2) The kidneys remove these form the body.
Deamination
Breakdown of amino acids.
–> Liver plays an important role in deamination of excess amino acids.
How does deamination occur?
-The hepatocytes (liver cells) dominate amino acids.
-They remove amino acid group and convert it first into ammonia (which is toxic) and then to urea (less toxic).
-The ammonia produced in deamination of proteins is converted into urea urea by a series of enzyme controlled reactions called ornithine cycle.
The kidney
The kidney control the water potential of the blood.
It acts as a fine filter for the blood:
1) Removing unwanted or excess products as urine:
-urea
-excess ions and water
2) Reabsorb products needed:
-glucose
-dissolved ions
-some water
General structure of the kidney
-Fibrous capsule: membrane which protects the kidney.
-Cortex: light coloured outer region.
-Medulla: darker coloured inner region.
-Ureter: carries urine to the bladder.
-Renal artery: supplies kidney with oxygenated blood.
-Renal vein: returns blood to the heart from kidney.
The nephron
-Kidney is made up of millions of tiny microscopic tubes called nephrons.
-There are 2 main types:
1) Cortical nephron (about 85% of human nephrons)
-Mainly found in renal artery.
-Have a loop of Henle that only just reaches into the medulla.
2) Juxtamedullary nephron
- Have a long loop of Henle that penetrates through the medulla.
- Are efficient at producing concentrated urine.
Nephron structure
-Proximal convoluted tubule (PCT): links Bowman’s capsule and loop of Henle. Surrounded by blood and capillaries.
-Loop of Henle: extends into the medulla of kidney. Surrounded by blood capillaries.
-Distal convoluted tubule (DCT): between loop of Henle and the collecting duct. Surrounded by fewer blood capillaries than the PCT.
-Collecting duct: DCT empties into this.
The first stage in osmoregulation: Ultrafiltration
-The first stage in the osmoregulation of the blood is ultrafiltration.
-The glomerulus and the Bowman’s capsule together make up the Malpighian body.
-Ultrafiltration is only the first step in the process.
-Most of the filtrate is later reabsorbed into the blood.
The process of ultrafiltration
-High blood pressure develops in the glomerular capillaries.
-The high pressure squeezes the blood out through the pores in the capillary wall.
-The cells of the Bowman’s capsule next to the capillaries act as an additional filter.
-The wall of the capsule is made up of special cells called podocytes.
-They have extensions called pedicels that wrap around the capillaries, forming slits that ensure any cells that have left the capillary do not get through into the tubule itself.
Selective reabsorption
After the ultrafiltrate has entered the nephron, the main function of the kidney tubule is to return most of what has been removed from the blood back.
The proximal convoluted tubule
-Over 80% of the glomerular filtrate is reabsorbed back into the blood in the first or proximal convoluted tubule (selective reabsorption).
–> The cells lining this tubule are covered with microvilli, which increase the surface area.
-The cells also contain a large number of mitochondrion (involved in active processes).
The contents of the ultrafiltrate in PCT
Glucose, amino acids, vitamins and most hormones are moved back into the blood by active transport.
-85% of the sodium chloride and water is reabsorbed as well.
-The sodium ions are actively transported.
-The chloride ions and water follow passively down the concentration gradients.
—> The blood is constantly moving through the capillaries, maintaining the concentration gradient for diffusion.
-By the time the filtrate reached the loop of Henle, it is isotonic with tissue fluid that surrounds the tubule.
The loop of Henle: Vasa recta
-Found in the medulla of the kidney in close contact with the network of capillaries known as the vasa recta.
-They create water potential gradient between the filtrate and the medullary tissue fluid that enables water to be reabsorbed from the DCT and collecting duct.
The loop of Henle: Countercurrent multiplier
-The creation if high concentration of sodium and chloride ions in the tissue fluid of the medulla is due to the flow of fluid is the opposite directions in the adjacent limbs of the loop of Henle.
-This creates a countercurrent multiplier, a biological system that uses active transport to set up and maintain concentration gradients.
The loop of Henle: The descending limb
-The descending limb is freely permeable to water but is not permeable to sodium and chloride ions.
-The fluid entering this limb is isotonic with the blood.
-The external concentration of sodium and chloride ions in the tissue fluid of the medulla and the blood in the vasa recta is higher.
-Water then moves out of the descending limb into tissue fluid by osmosis down a concentration gradient.
Extra feedback
-The release of ADH is also stimulated/inhibited by changes in blood pressure.
-Detected by baroreceptors.
-A rise in bp will suppress the release of ADH, so increase volume of water lost in urine.
-This causes bp to fall.
-A fall in bp (may indicate a loss of blood volume), can cause an increase in release of ADH, and the conservation of water by kidneys.
-water is returned to blood and a small amount of concentrated urine is produced.
Diabetes insipidus
-Diabetes mellitus (the most common form of diabetes; type 1&2), is the result of insufficient insulin being produced. Large volumes of urine containing sugar are produced.
-Diabetes insipidus (rare) is where individuals continuously produce large volumes of very dilute urine.
-Caused when an individual does not produce any ADH or kidneys don’t respond to ADH.
-Without ADH the DCT and collecting duct are permanently impermeable to water.
-Causes extreme thirst- individual needs to drink large quantities of water to avoid dehydration.
-Treated with drugs to replace ADH or enable to kidneys to produce more concentrated urine.
How do living organisms lose or gain heat?
-Small animals: large surface area-to-volume ratio; so they transfer energy more rapidly than larger organisms.
-There are several ways organisms warm up or cool down:
-warm up: by-product of metabolism. Chemical inefficiency means that energy is wasted, which warms the core of the organism.
-cool down: by evaporation of water from the body surfaces; sweating can increase cooling.
-energy may be transferred to/from environment by radiation.
-energy may be transferred to/from environment by convection. (Set up around hot objects, so adaptations to prevent cooling are common.
-energy may be transferred to/from environment by conduction (between the organism and the ground/water).
Ectotherms
-Rely heavily on external environment to control body temperature.
-Usually have behavioural and structural modifications that take advantage of environment in order to maintain a steady temperature.
-When cold: they may bask in the sun, press themselves against warm surfaces or have special areas of their skin to erect to maximise their absorption of radiation from the sun.
-When warm: they move into shade, or into mud/water. Panting allows evaporation of moisture in mouth.
-Need less food as metabolic rate is relatively low (aestivation) can become dormant (torpid).
Thermoregulation in endotherms: The skin
-Major homeostatic organ.
-Cooling takes place as water evaporates from surface of mouth and nose (can’t be prevented due to their moist surfaces).
Thermoregulation in endotherms; Keeping cool: Vasodilation
-A rich supply of capillaries runs near to the surface of the skin.
-Cooling by radiation, convection and conduction to the environment takes place from the blood flowing through the skin.
-The cooling is controlled via the arteriovenous shunt.
–> When exercising/external temperature rises the shunt is closed, allowing more blood to flow through the capillaries at the surface of the skin and vasodilation occurs (more energy is transferred to the environment by radiation).
Thermoregulation in endotherms; Keeping warm: Vasoconstriction
-The arteriovenous shunt int the blood supply to the skin opens, reducing blood flow through the capillaries.
-This is called vasoconstriction and it reduces energy lost from the surface of the skin.
Control of the core (blood) temperature: Drop in temperature
-If the temperature of the blood flowing through the hypothalamus drops, thermoregulatory centre reacts by sending nerve impulses through the autonomic nervous system to the skin.
-These cause a reduction in he blood flow through the capillaries in the skin, along with a reduction in the production of sweat and contraction of the erector pili muscles to raise the hairs.
-Impulses in autonomic motor neurons from thermoregulatory centre also stimulate involuntary contractions (shivering) and raise the amount of metabolic warming.
-∴ core temperature is maintained within very narrow limits.
Adaptations in colder climates
-Organisms are usually larger as this reduces their surface area-to-volume ratio (reduces their rate of cooling).
-Thick layers of fur/fat.
-Smaller extremities, eg. ears.
-Have countercurrent exchange systems which conserves heat.
–> Arterial blood is cooled as flows to the extremity and the venous blood is warmed as it returns to the body, minimising loss to the environment.
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Adaptations in warmer climates
-Have larger extremities (thin with a rich blood supply), eg. ears to increase energy transferred to the environment; elephants.
-Some can’t cool down enough to maintain a steady internal temperature and so can tolerate much larger fluctuations in body temperatures, eg. camels (also store water but do not sweat- saves water, but don’t have a major way of cooling down).
-Have countercurrent exchange system which helps to cool organs- mainly the brain.
–> Thermal energy is transferred from arterial blood to venous blood as they run close together. Cooled arterial blood supplied to the brain.
The Cape trough squirrel adaptations
-It has a flattened tail to keep its body shaded from direct sunlight.
-This keeps the body temperature down so that it can feed for long periods of the day.
