Urinary System (Unit 3) - Handwritten Notes
Download handwritten notes for Human Anatomy and Physiology 2 (Semester 2), covering Unit 3: The Urinary System. These notes detail the anatomy of the urinary tract, with special emphasis on the kidney and nephrons. They explain the functions of the kidneys and urinary tract, the physiology of urine formation, the micturition reflex, the role of the kidneys in acid-base balance, the Renin-Angiotensin System (RAS) in kidney function, and common disorders of the kidney. Available in PDF format.
Keywords: Urinary System, Kidney, Nephron, Urinary Tract, Urine Formation, Micturition Reflex, Acid-Base Balance, Renin-Angiotensin System (RAS), Kidney Disorders, Human Anatomy and Physiology, Handwritten Notes, PDF, Download, Semester 2, B.Pharm.
Urinary System (Unit 3) - Detailed Explanation
Anatomy of the Urinary Tract
The urinary system is responsible for filtering waste products from the blood and eliminating them as urine. It consists of:
- Kidneys (2): Bean-shaped organs located in the retroperitoneal space (behind the abdominal lining). They are the primary functional organs of the urinary system.
- Ureters (2): Tubes that carry urine from the kidneys to the urinary bladder.
- Urinary Bladder: A muscular sac that stores urine.
- Urethra: A tube that carries urine from the bladder to the outside of the body.
Anatomy of the Kidney
Each kidney has an outer renal cortex and an inner renal medulla. The medulla contains renal pyramids, cone-shaped structures whose tips (renal papillae) point towards the renal pelvis, a funnel-shaped cavity that collects urine. The renal pelvis connects to the ureter.
Anatomy of the Nephron
The nephron is the functional unit of the kidney. Each kidney contains about one million nephrons. A nephron consists of:
- Renal Corpuscle:
- Glomerulus: A network of capillaries where filtration of blood occurs.
- Bowman's Capsule (Glomerular Capsule): A cup-shaped structure that surrounds the glomerulus and collects the filtrate.
- Renal Tubule:
- Proximal Convoluted Tubule (PCT): The first part of the tubule, where most reabsorption of water, ions, and nutrients occurs.
- Loop of Henle (Nephron Loop): A U-shaped loop that extends into the renal medulla. It plays a key role in concentrating urine. It has a descending limb and an ascending limb.
- Distal Convoluted Tubule (DCT): Further reabsorption and secretion occur here, regulated by hormones.
- Collecting Duct: Receives fluid from multiple nephrons and carries it to the renal pelvis. Water reabsorption is regulated here by antidiuretic hormone (ADH).
Functions of the Kidney and Urinary Tract
Key functions include:
- Filtration: Filtering blood to remove waste products (urea, creatinine, uric acid), excess ions, and water.
- Reabsorption: Reabsorbing essential substances (glucose, amino acids, water, ions) back into the bloodstream.
- Secretion: Secreting certain substances (e.g., drugs, toxins, hydrogen ions) from the blood into the renal tubules.
- Regulation of blood volume and blood pressure: By controlling water reabsorption.
- Regulation of blood pH: By controlling the excretion of hydrogen ions (H+) and bicarbonate ions (HCO3-).
- Production of hormones: Erythropoietin (stimulates red blood cell production) and calcitriol (active form of vitamin D).
- Excretion: Eliminating waste products in the form of urine.
Physiology of Urine Formation
Urine formation involves three main processes:
- Glomerular Filtration: Blood pressure forces water and small solutes (e.g., ions, glucose, amino acids, waste products) from the glomerular capillaries into Bowman's capsule. Large molecules (proteins, blood cells) are retained in the blood. The fluid in Bowman's capsule is called the glomerular filtrate.
- Tubular Reabsorption: Essential substances are reabsorbed from the renal tubules back into the blood. This occurs primarily in the proximal convoluted tubule, but also in the loop of Henle, distal convoluted tubule, and collecting duct. Reabsorption can be active (requiring energy) or passive (diffusion).
- Tubular Secretion: Certain substances are actively secreted from the blood into the renal tubules. This helps eliminate waste products and regulate blood pH.
Micturition Reflex
Micturition is the process of urination. The micturition reflex is a spinal reflex that controls the emptying of the urinary bladder. As the bladder fills with urine, stretch receptors in the bladder wall are activated. This sends signals to the spinal cord, which triggers the parasympathetic nervous system to:
- Contract the detrusor muscle (the smooth muscle of the bladder wall).
- Relax the internal urethral sphincter (smooth muscle).
The external urethral sphincter (skeletal muscle) is under voluntary control. When it's relaxed, urination occurs.
Role of Kidneys in Acid-Base Balance
The kidneys play a crucial role in maintaining blood pH within a narrow range (7.35-7.45). They do this by:
- Reabsorbing bicarbonate ions (HCO3-): Bicarbonate is a major buffer in the blood, helping to neutralize acids. The kidneys reabsorb most of the filtered bicarbonate.
- Secreting hydrogen ions (H+): When the blood is too acidic (acidosis), the kidneys secrete H+ into the urine.
- Generating new bicarbonate ions: When needed.
Role of RAS in Kidney Function
The Renin-Angiotensin System (RAS) is a hormone system that plays a key role in regulating blood pressure and fluid balance.
- Renin: An enzyme released by the kidneys (from juxtaglomerular cells) in response to low blood pressure, low blood volume, or low sodium levels.
- Angiotensinogen: A protein produced by the liver. Renin converts angiotensinogen to angiotensin I.
- Angiotensin-Converting Enzyme (ACE): An enzyme found primarily in the lungs. ACE converts angiotensin I to angiotensin II.
- Angiotensin II: A potent vasoconstrictor (narrows blood vessels), increasing blood pressure. It also stimulates the release of aldosterone from the adrenal glands.
- Aldosterone: A hormone that acts on the kidneys to increase sodium reabsorption (and therefore water reabsorption), increasing blood volume and blood pressure.
Disorders of the Kidney
Common kidney disorders include:
- Kidney Stones (Nephrolithiasis): Hard deposits that form in the kidneys.
- Urinary Tract Infections (UTIs): Bacterial infections of the urinary tract.
- Glomerulonephritis: Inflammation of the glomeruli.
- Chronic Kidney Disease (CKD): A gradual loss of kidney function.
- Polycystic Kidney Disease (PKD): A genetic disorder characterized by the growth of cysts in the kidneys.
- Acute Kidney Injury (AKI): A sudden loss of kidney function.
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