Kidney Function and Nephron Quiz

• Communication is essential for organisms to detect and respond to internal and external environmental changes.
• Survival in multicellular organisms relies on nervous and endocrine systems for change management.

Cell Signalling

• Cell signalling involves communication between cells via electrical signals (neurones) or hormones.
• Neuronal cell signalling is faster and short-term, while chemical signalling is slower and long-term.
• Endocrine signalling is for long distances, using the circulatory system.
• Paracrine signalling occurs locally between cells, directly or with extracellular fluid.
• Autocrine signalling involves a cell stimulating its own receptors by releasing signals.

Homeostasis

• Homeostasis maintains a constant internal environment, including temperature, water potential, pH, and blood glucose.
• Homeostasis is achieved through negative feedback, counteracting changes to restore optimum conditions.
• Key elements for negative feedback include sensory receptors and effectors.
• Sensory receptors detect changes and relay messages via nervous or hormonal systems to effectors, which initiate responses.
• Positive feedback amplifies original changes, exemplified by cervix dilation during childbirth.

Thermoregulation

• Ectotherms regulate body temperature via external sources, lacking the ability to increase internal heat production through respiration and they control body temperature by exchanging heat with their surroundings,
• Endotherms maintain constant body temperature independently of the external temperature.
• Endotherms contain thermoreceptors, which monitor core body temperature changes and the thermoreceptors communicate these them to the hypothalamus.
• The hypothalamus coordinates physiological or behavioural responses.

Actions Taken by Endotherms

• Shivering: Muscle contractions stimulated by the hypothalamus increase temperature by releasing heat.
• Sweat glands: Sweat production cools the body through evaporation.
• Hairs on skin: Flattening hairs minimizes insulation and increases heat loss, while raising them provides insulation.
• Arterioles: Dilation increases heat loss as blood flows closer to the skin, while constriction reduces heat loss.

Deamination of Amino Acids

• The liver breaks down excess amino acids from protein digestion, because nitrogenous substances are damaging to the body
• Deamination, the removal of the amino group from excess amino acids, forms ammonia and organic acids.
• Organic acids are used in respiration to produce ATP or are converted to carbohydrates and stored as glycogen.
• Ammonia is converted to urea in the ornithine cycle.
• Urea is released into the blood, filtered by the kidneys, and excreted as urine.

Kidneys

• Kidneys excrete waste products, especially urea in urine.
• Blood enters the kidney via the renal artery and passes through capillaries in the cortex.
• Blood enters the glomerulus through the afferent arteriole and exits through the narrower efferent arteriole, creating high pressure in the glomerulus in order to push smaller molecules (glucose, urea, water and sodium) into the Bowman's capsule during ultrafiltration..
• Selective reabsorption occurs in the proximal convoluted tubule, where useful substances like amino acids, glucose, and vitamins are reabsorbed.
• Sodium ions and glucose are cotransported, and water re-enters the blood following the water potential gradients resulting from the cotransport.
• Excreted substances pass through tubules and the ureter into the bladder.
• Filtered blood exits the kidneys via the renal vein.

Control of Water Potential of the Blood

• During dehydration, less water is reabsorbed in the loop of Henle, distal convoluted tubule, and collecting duct, resulting in concentrated urine.
• Hormones regulate water reabsorption.
• Osmoreceptors in the hypothalamus monitor water potential.
• If low water content is detected, the hypothalamus signals the pituitary gland to release ADH.
• ADH increases the permeability of the DCT and collecting duct to allow water to be reabsorbed from the tubules into the blood.
• Concentrated urine is produced to prevent water loss.
• Aquaporins in vesicle membranes increase cell surface permeability to water.
• In the case of the body being being well hydrated, the opposite processes occur.
• This balance of water potential is called osmoregulation.

Blood Glucose Regulation

• Maintaining blood glucose levels, around 90mg per 100cm3 of blood, is crucial for processes like brain cell respiration.
• High glucose levels lead to excretion in urine, preventing storage as glycogen or fat.
• Beta cells in the pancreas detect increased glucose after a high-carbohydrate meal.
• Insulin is released by beta cells, which inhibits alpha cell action
• Insulin acts on target hepatocytes in the liver, fat, and muscle cells.
• Insulin binds to receptors on the cell membrane and causes adenyl cyclase to convert ATP into cyclic AMP (cAMP)
• cAMP, a secondary messenger, activates enzymes to open glucose channels in the cell membrane, allowing glucose to enter and be converted to glycogen or fats for storage and later respiration.

Low Blood Glucose

• Alpha cells detect low glucose and secrete glucagon, which inhibits beta cell action.
• Glucagon binds to receptors on the cell surface membrane which causes a conformational change
• G-proteins are activated, which activate adenylyl cyclase enzymes
• cAMP, a secondary messenger forms
• Protein kinases are then activated, initiating a cascade of enzymes
• The final enzyme that is activated is glucagon which stimulates the hepatocytes to convert glycogen to glucose
• Glucose then diffuses out of hepatocytes into the blood
• Cells use fatty acids and amino acids for respiration instead

Second Messenger Model of Adrenaline

• Perceived threats trigger adrenaline release, causing pupil dilation, digestive system inhibition, increased heart rate/stroke volume, increased blood flow to the brain, and increased metabolism.
• Adrenaline interacts with adrenergic receptors on the cell surface.
• Adrenaline, released from the adrenal gland binds to receptors, activates adenyl cyclase.
• Activated enzyme converts ATP to cyclic AMP (cAMP), a second messenger.
• cAMP activates protein kinase A, triggering glycogen breakdown into glucose for energy and to provide increased mental awareness.
• The primary messenger is adrenaline.
• The secondary messenger is cAMP.

Homeostasis in Plants

• Stomatal aperture is regulated for carbon dioxide uptake and water conservation.
• Stomata have daily rhythms, responding to environmental changes to control carbon dioxide diffusion and water loss (transpiration).
• Guard cells control stomata opening and closing by inflating for gas exchange or deflating to prevent water loss.
• Potassium ion influx increases turgidity inflates stomata
• Excess water loss triggers stomatal closing, often due to low light levels and reduced photosynthesis.
• In roots, abscisic acid is produced in response to decreasing water potential or stress and then activates calcium ions (a secondary messanger) to close stomata.
• Guard cells are sensitive to calcium ion changes.

Test your knowledge of kidney function. This quiz covers efferent arterioles, selective reabsorption, osmoreceptors, glomerular pressure, and the loop of Henle. Assess your understanding of hormonal regulation and nephron structure.