Human Anatomy: Kidney Functions Quiz

Urinary System II

• Kidneys contain approximately one million nephrons, which are the functional units.
• Nephrons consist of tubules and associated blood vessels.
• Plasma filters in the glomerular capsule.
• Glomerular filtrate moves to the tubules. Tubular reabsorption removes most water, ions, and nutrients from the filtrate.
• Tubular secretion moves ions and toxic chemicals from blood into the tubules.

Lecture Outcomes

• Students will understand how the kidneys maintain water balance.
• Students will learn about disorders/diseases of the urinary system.

Kidneys and Homeostasis

• Kidneys maintain water balance.
• Kidneys maintain salt balance.
• Kidneys secrete an enzyme involved in controlling blood volume and blood pressure (angiotensin).
• Kidneys maintain acid-base balance and blood pH.
• Kidneys regulate red blood cell production via erythropoietin.
• Kidneys activate an inactive form of vitamin D, aiding calcium absorption.

Producing Dilute or Concentrated Urine

• The urinary system maintains fluid homeostasis.
• Kidneys adjust the amount of water leaving the body based on urine concentration.
• High solute concentration in the renal medulla drives the process.
• Kidney adjust collecting duct and distal tubule permeability depending on antidiuretic hormone (ADH) levels.

Producing Dilute Urine

• Mechanism: absence of ADH, distal tubules are impermeable to water, water doesn't reabsorb.
• Water diffuses out of the descending limb of the loop of Henle.
• The first part of the ascending limb is permeable to salt and urea but not water.
• Salt (NaCl) reabsorption occurs without water reabsorption in the ascending limb.
• Urea is diffused from the collecting tubule into the ascending limb.
• The last part of the ascending limb is impermeable to water and salt.
• Active salt transport occurs without simultaneous water reabsorption continuing in the distal and collecting ducts.
• High-volume, dilute urine is formed.

Producing Concentrated Urine

• Mechanism: Presence of ADH, increased permeability of collecting ducts to water.
• More water is reabsorbed.
• The medulla has a high solute and low water concentration.
• Small volume of concentrated urine is excreted.

ADH Regulates Water Balance

• Antidiuretic hormone is produced in the posterior pituitary gland.
• Blood volume depends on water in the body.
• Changes in water lead to changes in blood volume and blood pressure.
• Kidneys, hypothalamus, and posterior pituitary control homeostasis of blood volume.
• Hypothalamus synthesizes ADH.
• Posterior pituitary releases ADH.
• Kidneys respond to ADH changes.
• Negative feedback regulates blood solute concentration.
• This involves increasing or decreasing ADH secretion.
• Thirst response may also change.

Negative Feedback Loop

• Blood solute concentration rises, neurons in the hypothalamus make ADH.
• ADH goes into the blood stream, reaching the kidneys.
• Increases permeability of collecting ducts to water and decreased loss of water in urine.
• Scenario 2 (solute concentration decreases):

1. Hypothalamus signals pituitary to release less ADH.
2. Collecting duct is less permeable to water,.
3. Excess water is excreted.
4. Person feels less thirsty

Diuretics

• High urine flow rate is called diuresis.
• A substance that promotes diuresis is a diuretic.
• Lasix (furosemide) reduces blood volume and blood pressure used in hypertension treatment.
• Caffeine is a mild diuretic, inhibiting sodium reabsorption and promoting water retention.
• Alcohol inhibits ADH release and makes collecting ducts less permeable to water.

Kidney Stones

• Kidney stones form when minerals in the urine crystallize into solid masses.
• Small stones are excreted in urine.
• Large stones can block the ureter, causing decreased urine flow and intense pain.
• Removed using ultrasonic shock waves or surgically.

UTIs

• UTIs are infections in any part of the urinary system usually caused by bacteria.
• Symptoms include burning/pain during urination.
• Bacteria can travel to kidneys.
• Treated with antibiotics.

Renal Failure and Dialysis

• Kidney failure means kidneys cannot properly filter blood.
• Artificial help using a dialysis machine to filter blood.
• The machine mimics kidney nephrons using semipermeable membrane with clean dialysis fluid.
• Metabolic wastes and ions diffuse into the dialysis fluid.

Review

• Kidneys maintain water balance, impacting blood volume and pressure.
• Low blood solute concentration decreases ADH secretion and increases permeability which leads to excretion of dilute urine.
• High blood solute concentration increases ADH secretion and increases kidney permeability to water leading to concentrated urine excretion.

Endocrine System I

• Endocrine system consists of specialized duct-less tissue and glands that secrete hormones, chemical messengers, controlling various body functions.

Endocrine System Components

• Includes the hypothalamus, pituitary gland, pineal gland, thyroid gland, parathyroid glands, thymus gland, heart, stomach, pancreas, intestines, ovaries, and testes. (and several hormones)

Hormones

• Chemical messengers carried by blood.
• Act only on target cells.
• Ensures specificity of hormone action.
• Hormones can be lipid-soluble (steroid) or non-lipid-soluble.

Steroid Hormones

• Related to cholesterol.
• Lipid-soluble.
• Diffuse easily across the lipid bilayer.
• Bind to intracellular receptors.

Non-Steroid Hormones

• Related to proteins.
• Lipid-insoluble.
• Cannot cross the lipid bilayer.
• Bind to receptors on the cell surface.

Steroid Hormone Action

• Diffuses across the cell membrane and binds to receptor.
• Hormone-receptor complex binds to DNA triggering gene activation resulting in protein formation.
• Proteins are synthesized which carry out cellular responses.

Non-Steroid Hormone Action

• Hormone binds cell-surface receptors initiating a change to the cell.
• Activates secondary messenger (like cyclic AMP).
• A cascade of enzyme activation happens.
• The final product from enzymatic reactions is created.

Exocrine vs Endocrine Glands

• Exocrine glands secrete products into ducts. Example includes sweat, saliva, and milk.
• Endocrine glands secrete hormones directly into interstitial fluid, lymph, and the blood. Example includes adrenaline and estrogen.
• Liver and pancreas act as both, with exocrine function in digestive processes and an endocrine function in hormone secretion.

Hormones (continued)

• Hormones are chemical messengers acting on target cells.
• They trigger cellular responses.
• Endocrine system is slower than the nervous system due to release into the bloodstream.

Practice Questions

• Question 1: Sweating depletes water, causing a rise in blood solute concentration. This triggers the thirst response increasing water intake to restore balance.

• Question 2: The nervous system is responsible for quick reflexes like withdrawing a foot when stepping on a nail.

• Question 3: The incorrect statement is "b" (during tubular reabsorption, useful substances move from the blood into the filtrate). In reality, in reabsorption, useful substances move from the filtrate to the blood within the nephron.