16.5 - Control Of Blood Water Potential — Structure Of The Nephron Flashcards
Define osmoregulation and explain its importance in homeostasis.
- Definition: Osmoregulation is the homeostatic control of the water potential of the blood.
- Importance: It ensures the optimum concentration of water and salts is maintained in the blood plasma and tissue fluid, which is crucial for maintaining a fairly constant water potential
Describe the structure and location of the kidneys in mammals.
- Mammals have two kidneys located at the back of the abdominal cavity, one on each side of the spinal cord.
A section of the kidney reveals:
- Fibrous capsule: Outer membrane that protects the kidney.
- Cortex: Lighter-coloured outer region containing renal (Bowman’s) capsules, convoluted tubules, and blood vessels.
- Medulla: Darker-coloured inner region containing loops of Henle, collecting ducts, and blood vessels.
- Renal pelvis: Funnel-shaped cavity collecting urine into the ureter.
- Ureter: Tube that carries urine to the bladder.
- Renal artery: Supplies blood to the kidney from the heart via the aorta.
- Renal vein: Returns blood from the kidney to the heart via the vena cava
What is the nephron, and why is it significant?
- The nephron is the functional unit of the kidney.
- It is a narrow tube up to 14mm long, closed at one end, and consists of two twisted regions separated by a long hairpin loop.
- Each kidney contains around one million nephrons, which are the basic structural and functional units responsible for filtration, reabsorption, and excretion.
Describe the structure and function of the renal (Bowman’s) capsule.
- The renal capsule is the closed, cup-shaped end at the start of the nephron.
- It surrounds a mass of blood capillaries called the glomerulus.
- Its inner layer consists of specialised cells called podocytes, which aid in filtration by creating small slits through which fluid passes.
What is the role of the proximal convoluted tubule, and how is it adapted for its function?
- The proximal convoluted tubule is a series of loops surrounded by blood capillaries.
- Its walls are made of epithelial cells with microvilli, which increase the surface area for the reabsorption of substances such as glucose, water, and salts from the filtrate back into the blood.
Explain the structure and significance of the loop of Henle
- The loop of Henle is a long, hairpin-shaped loop extending from the cortex into the medulla and back.
- It is surrounded by blood capillaries.
- The loop plays a crucial role in the reabsorption of water and the creation of a concentration gradient in the medulla, enabling water conservation in the kidney.
Differentiate between the distal convoluted tubule and the proximal convoluted tubule.
Both are series of loops surrounded by blood capillaries, but:
- Proximal convoluted tubule: Surrounded by many capillaries and contains epithelial cells with microvilli to maximise reabsorption.
- Distal convoluted tubule: Surrounded by fewer capillaries, its main role is to make finer adjustments to water and salt levels under the influence of hormones like ADH and aldosterone.
What is the collecting duct, and what is its role in osmoregulation?
- The collecting duct is a tube into which multiple distal convoluted tubules empty.
- It is lined with epithelial cells and widens as it approaches the renal pelvis.
- It plays a key role in the reabsorption of water under the influence of antidiuretic hormone (ADH) to regulate the body’s water balance.
Describe the blood vessels associated with each nephron.
- Afferent arteriole: A tiny vessel arising from the renal artery that supplies the nephron with blood.
- Glomerulus: A knot of capillaries where fluid is forced out of the blood under high pressure.
- Efferent arteriole: A vessel leaving the glomerulus with a smaller diameter than the afferent arteriole, creating high blood pressure.
- Blood capillaries: A network surrounding the proximal convoluted tubule, loop of Henle, and distal convoluted tubule, enabling the reabsorption of water, salts, and glucose.
Explain the role of the glomerulus in filtration.
- The glomerulus is a many-branched knot of capillaries inside the renal capsule.
- High blood pressure, caused by the smaller diameter of the efferent arteriole compared to the afferent arteriole, creates hydrostatic pressure that forces fluid out of the blood.
- The filtrate, containing water, salts, glucose, and urea, passes into the renal capsule while larger molecules like proteins remain in the blood.
