Urinary System - Lecture notes 11 PDF

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Covers essentials for Human Anatomy and Physiology final exam...

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1 Urinary System Objectives: highlighted in yellow!! 1. Briefly describe the structure and function of the organs of the urinary system. Start off with general FUNCTIONS of the Urinary system: 1. Regulates aspects of homeostasis (acronym = “web pram”) • Water balance • Electrolytes balance • Acid-base balance in the blood • Blood pressure • Red blood cell production • Metabolism of vitamin D • Production of hormones 2. Elimination of waste products • Nitrogenous wastes • Toxins • Drugs Reminder: What is an ELECTROLYTE? Charged particles (ions) that conduct electrical currents e.g. Calcium, potassium, sodium • Most enter the body via food and water. • Correct balance of electrolytes must be present in the Intra/Extra Cellular Fluid. • Kidneys are the major factor in regulating electrolyte balance.

3. Characteristics of Urine Used for Medical Diagnosis • Yellow coloured due to the pigment urochrome (from the destruction of

2 hemoglobin) and solutes • Sterile • Slightly aromatic • Normal pH of around 6 • Presence of vitamin B changes the colour STRUCTURE of the organs of the urinary system • Kidneys • Ureters • Urinary bladder • Urethra

Urethra • Carries urine from bladder to genitals and exterior by peristalsis & relaxation/contraction sphincter muscles. • 2 sphincters: 1 internal – involuntary smooth muscle 1 external – voluntary skeletal muscle • Female - 3-4 cms • Male – 20-25 cms • In males, the urethra travels through the penis, and carries semen as well as urine. • In females, the urethra is shorter and emerges above the vaginal opening. • Women are more susceptible to Urinary tract infections, etc due to short length and microbes being able to ascend.

3 Bladder • Smooth muscular sac for temporary storage of urine. • Anterior to rectum. • Anterior to uterus in female. • Sits on the pelvic floor • Prostate gland in males surrounds the bladder neck. • Empty bladder – roughly 5 - 7.5cms long. • Moderately full – roughly 12.5cms. Holds between 500-1000mls • Contains 3 openings: 2 x ureter orifices + urethra • 3 layers of muscle tissue: inner to outer = Mucosa, Sub mucosa, Peritoneum Ureters • Humans have 2 – approx 25-30cms in length, 6mm thick. • Extend from the Hilus of each kidney to posterior surface of the bladder at an oblique angle. • Tubes that convey urine, formed in the kidneys, to the urinary bladder utilising peristalsis and gravity.

Kidneys • 2 kidneys– bean shaped • Attached to the abdominal wall by a fatty capsule • Protected by the floating ribs (11th and 12th) • Blood vessels and nerves enter and leave through a central point - the hilus • The Adrenal glands lay on the superior surface of each kidney. • Filter roughly 180L of blood daily •Renal capsule, adipose capsule, renal fascia

4 Each has 3 regions Important! • 1. Outer renal cortex where most of the 1 million functional units (nephrons) are located • 2. Inner renal medulla (middle) made up of renal pyramids (collecting ducts) separated by renal columns (remaining nephrons) • 3. Major calyces and renal pelvis (basin). Collect and direct urine to ureter

Nephron • The structural and functional units of the kidneys • Responsible for forming urine • Most kidneys house over 1 million • Main structures of the nephrons: 1. Glomerular capsule 2. Renal tubule

Glomerular capsule The Glomerulus is found inside the Glomerular capsule (or Bowman’s capsule)

5 • A specialized capillary bed that sits within the glomerular capsule • Designed to function as a mechanical filter •Large afferent (afferent = arriving) arteriole •Narrow efferent (efferent = exiting) arteriole •Efferent arteriole turns into peri tubular capillaries which wrap around the renal tubule

Renal Tubule • Glomerular (Bowman’s) capsule • Proximal convoluted tubule • Loop of Henle • Distal convoluted tubule

Peritubular Capillaries • Efferent arteriole leaves the glomerulus, narrows into capillaries and wraps around the renal tubule. • Substances can then move either from the tubule into the capillary or visa versa

Nephron overview

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Awesome website to check out: http://faculty.southwest.tn.edu/rburkett/A%26P2%20urinary_system.htm 2. Outline the process of urine formation including filtration, reabsorption and secretion. Formation of urine - Involves 3 processes: • Filtration • Reabsorption • Secretion

Filtration • Non-selective passive process – no ATP required.

7 • Water and solutes smaller than proteins are forced through the filtration membrane of glomerulus by hydrostatic pressure • Blood cells and proteins are too large to pass through the filtration membrane • Filtrate (substance from blood) is collected in the glomerular capsule and enters the renal tubule

Reabsorption • The peritubular capillaries reabsorb several materials the body can make use of: •Some water •Glucose •Amino acids •Ions (e.g. 65% of sodium) • Some reabsorption is passive, most is active • Most reabsorption occurs in the proximal convoluted tubule (start of tubule) Materials Not Reabsorbed • Nitrogenous waste products •Urea •Uric acid •Creatinine (by-product of muscle metabolism) • Excess water

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Secretion (reabsorption in reverse) • Some materials move from the peritubular capillaries into the renal tubules •Hydrogen, bicarbonate and potassium ions •Creatinine •Drugs (e.g. penicillin) • Materials left in the renal tubule move toward the ureter

Maintaining Water Balance Kidneys ‘juggle’ water balance…… • Large amounts of dilute urine is produced if water intake is excessive • Smaller amounts of concentrated urine is produced if large amounts of water are lost or not put into the body • Adequate concentrations of various electrolytes must be present

3. Outline the micturition reflex Micturition (proper word for urination) Reflex

9 1. Bladder fills up with urine, stretching the bladder activates stretch receptors to be stimulated/excited 2. Increased activity of sensory neurons, which synapse with motor neurons in the sacral spinal cord, to make bladder contract 3. Contraction forces stored urine past internal sphincter (involuntary muscle) and signals to central nervous system (brain) that micturition needs to take place 4. Voluntary control of external sphincter relaxation controls whether micturition is convenient....