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Chapter 24: Urinary System

Chapter 24: Urinary System. Excretion. Organs of excretion: Kidneys Sweat glands Lungs Intestines. Urinary System Organs. Kidneys (2) Ureters (2) Urinary bladder (1) Urethra (1). Kidneys. Location: retroperitoneal, high on the posterior wall of the abdominal cavity

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Chapter 24: Urinary System

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  1. Chapter 24: Urinary System

  2. Excretion • Organs of excretion: • Kidneys • Sweat glands • Lungs • Intestines

  3. Urinary System Organs • Kidneys (2) • Ureters (2) • Urinary bladder (1) • Urethra (1)

  4. Kidneys • Location: retroperitoneal, high on the posterior wall of the abdominal cavity • Structure: reddish-brown, beanlike shape, enclosed in a tough fibrous capsule; three distinct regions: • Renal cortex • Renal medulla • Renal pelvis

  5. Blood Supply • Blood supply: renal artery, which arises from the abdominal aorta; renal vein, which empties into the inferior vena cava

  6. Nerve Supply • Nerve supply: renal nerves; primarily sympathetic nerves

  7. Kidney Functions • Excrete nitrogenous waste (urea, uric aid, ammonia, and creatinine) • Regulate blood volume by determining the amount of water excreted • Help regulate the electrolyte content of the blood • Play a major role in the regulation of acid-base balance by controlling the excretion of H+ • Play a role in regulation of blood pressure • Play a role in regulation of RBC production

  8. Urine Making: The Nephron Unit • Nephron: functional unit of the kidney; two parts: • Renal tubules: • Bowman’s capsule • proximal convoluted tubule • loop of Henle • distal convoluted tubule • collecting duct

  9. Urine Making: The Nephron Unit The nephron unit: tubular structures.

  10. Urine Making: The Nephron Unit 2. Renal blood vessels: • renal artery • afferent arteriole • glomerulus • efferent arteriole • peritubular capillaries • renal vein

  11. Process of Urine Formation • Three steps: • Glomerular filtration • Tubular reabsorption • Tubular secretion

  12. Step 1: Glomerular Filtration • Water & dissolved substances move from glomerulus into Bowman’s capsule. • caused by the blood pressure difference between glomerulus & Bowman’s capsule • Glomerular filtrate: water and dissolved substances filtered into Bowman’s capsule • Glomerular filtration rate (GFR): rate at which glomerular filtration occurs

  13. Step 2: Tubular Reabsorption • Process by which glomerular filtrate moves from the tubules into the blood of the peritubular capillaries • Diuresis: excess secretion of urine • Diuretics: drugs that increase the production of urine

  14. Step 3: Tubular Secretion • Process by which small amounts of substances from the peritubular capillaries move into the tubules • Secreted substances: potassium ions, hydrogen ions, uric acid, ammonium ions, and drugs

  15. Hormones That Work on the Kidneys • Aldosterone • Antidiuretic hormone (ADH) • Natriuretic peptides • Atrial natriuretic peptide (ANP) • Brain natriuretic peptide (BNP) • Parathyroid hormone

  16. Aldosterone • Secreted by adrenal cortex and acts primarily on the distal tubule • Stimulates the reabsorption of sodium and water and the excretion of potassium; “salt retaining” hormone • Increases blood volume and blood pressure • Released after the renin-angiotensin-aldosterone system is complete.

  17. How Aldosterone is Released… • When B/P drops: • Renin (enzyme) is released from cells • Triggers liver to release Angiotensinogen (protein) which forms Angiotensin I (protein) • ACE changes Angiotensin I to Angiotensin II (protein) • Angiotensin II stimulates secretion of Aldosterone (hormone from adrenal cortex) • Na+ and H2O reabsorbed= BP elevates

  18. Antidiuretic hormone (ADH) • Secreted by the posterior pituitary gland and works primarily on the collecting duct • Stimulates the reabsorption of water into blood • Plays a role in determining blood volume and blood pressure • Release is stimulated by a decrease in blood volume and an increase in the concentration of solutes in the plasma • ADH present=collecting duct becomes permeable to water=water reabsorbed into blood=concentrated urine and greater blood volume.

  19. Natriuretic peptides • Cause natriuresis, excretion of sodium (Na+); • When released, it causes a decrease of aldosterone secretion; Na+ and water are then excreted in urine • Atrial natriuretic peptide (ANP): secreted by the walls of the atria of the heart in response to an increase in the volume of blood • Brain natriuretic peptide (BNP): secreted by the walls of the ventricles in response to elevated ventricular pressure • Opposite effect of aldosterone and ADH

  20. Parathyroid hormone (PTH) • Secreted by the parathyroid glands • Plays an important role in the regulation of two electrolytes: calcium and phosphate • Stimulates the renal tubules to reabsorb calcium and excrete phosphate to tubules • Release stimulated by low plasma level of calcium

  21. Characteristics of Urine • Amount (volume): average 1500 ml/24 hours • pH: average 6.0 • Specific gravity: slightly heavier than water (1.001 to 1.035) • Color: yellow (amber, straw colored, deep yellow in dehydration, pale yellow with overhydration)

  22. Dialysis • Uremia: “urine in blood”; kidneys no longer make urine and blood is not cleansed of its waste • Dialysis: artificial method of cleansing the blood • Artificial kidney • Peritoneal dialysis

  23. Your Plumbing • Urinary tract: • Ureters: connect the kidneys and bladder • Urinary bladder: temporary reservoir for storage of urine • Urethra: tube that carries urine from the bladder to the outside

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