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Anatomy and Physiology 2

by: Ashlee Wilson

Anatomy and Physiology 2 BIOL 2020

Marketplace > University of Memphis > Biology > BIOL 2020 > Anatomy and Physiology 2
Ashlee Wilson
University of Memphis
GPA 3.3

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Chapter 26 notes
Human Anatomy and Physiology II
Martha Brown
Class Notes
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This 6 page Class Notes was uploaded by Ashlee Wilson on Monday April 18, 2016. The Class Notes belongs to BIOL 2020 at University of Memphis taught by Martha Brown in Spring 2016. Since its upload, it has received 6 views. For similar materials see Human Anatomy and Physiology II in Biology at University of Memphis.

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Date Created: 04/18/16
A&P Chapter 26 The Urinary System Urinary System  Consists of the kidneys, ureters, bladder, and urethra.  Maintains homeostasis by managing the volume and composition of fluid reservoirs, primarily blood. Homeostatic Kidney Functions  Regulation of blood ionic composition: Na+, K+, Cl-.  Regulation of blood pH: H+, HCO-3.  Regulation of blood volume: H2O.  Regulation of blood pressure.  Maintenance of blood osmolarity.  Production of hormone: Calcitrol & Erythropoietin.  Excretion of metabolic waste and foreign substances ( drugs or toxins). Renal Anatomy  The kidneys are retroperitoneal, partly protected by the lower ribs.  Intended area is called the Hilum.  This is an entrance for: Renal artery, Renal vein, Ureter, Nerves, & Lymphatics. External Layers  Connective Tissue, Superficial to Deep: Renal Fascia- Anchors to other structures, Adipose Capsule- Protects and anchors, & Renal Capsule- Continuous with Ureter. Internal Renal Anatomy  Renal Cortex – Outer layer.  Renal Medulla – Inner region.  Renal Pyramids – Secreting Apparatus and Tubules.  Renal Columns – Anchor the Cortex.  Papillary ducts empty urine into calyces.  Calyces pass urine to the Ureter. Blood and Nerve supply of the Kidneys  Blood supply- Although kidneys constitute less than 0.5% of total body mass, they receive 20–25% of resting cardiac output.  Nerve supply- Renal Nerves primarily carry sympathetic outflow & They regulate blood flow through the kidneys. The Nephron  Renal corpuscle filters the blood plasma.  Renal tubule modifies the filtrate. The Renal Corpuscle  The Renal Corpuscle consists of two parts:  The Glomerulus is a mass of capillaries.  The Glomerular (Bowman’s) Capsule has a visceral layer of podocytes which wrap around the capillaries.  The Glomerulus is a mass of capillaries.  It is fed by the Afferent Arteriole and drains into the Efferent Arteriole.  Mesangial cells are contractile and help regulate glomerular filtration.  The Glomerular (Bowman’s) Capsule has a visceral layer of podocytes which wrap around the capillaries.  The filtrate is collected between the visceral and parietal layers.  The glomerular endothelial cells have large pores (fenestrations) and are leaky.  Basal lamina lies between endothelium and podocytes.  Podocytes form pedicels, between which are filtration slits.  The filtrate passes from the glomerular capsule to the renal tubule. The Juxtaglomerular Apparatus  The ascending loop contacts the afferent arteriole at the macula densa.  The wall of the arteriole contains smooth muscle cells, juxtaglomerular cells.  The apparatus regulates blood pressure in the kidney in conjunction with the ANS. The Distal Collecting Tubule and Collecting Duct.  Principal Cells – receptors for ADH and aldosterone.  Intercalated Cells – help to manage blood pH. Two Kinds of Nephrons  Cortical nephrons- 80-85% of nephrons.  Renal corpuscle in outer portion of cortex.  Short loops of Henle extend only into outer region of medulla.  Create urine with osmolarity similar to blood. Juxtamedullary Nephrons  Renal corpuscle deep in cortex with long nephron loops  Receive blood from peritubular capillaries and vasa recta  Ascending limb has thick and thin regions  Enable kidney to secrete very concentrated urine Glomerular Filtration  Driven by blood pressure  Opposed by capsular hydrostatic pressure and blood colloid osmotic pressure  Water and small molecules move out of the glomerulus.  In one day, 150–180 liters of fluid pass out of the blood into the glomerular capsule.  Glomerular filtration rate – amount of filtrate formed by both kidneys each minute  Homeostasis requires kidneys to maintain a relatively constant GFR  Too high – substances pass too quickly and are not reabsorbed  Too low – nearly all reabsorbed and some waste products not adequately excreted  GFR averages 125mL/min in males and 105mL/min in females  Controlled by: Renal Autoregulation, Neural Regulation, & Hormonal Regulation Renal Autoregulation  Myogenic Mechanism- Smooth muscle cells in afferent arterioles contract in response to elevated blood pressure.  Tubuloglomerular Feedback- High GFR diminishes reabsorption, Macula Densa inhibits release of nitric oxide, & Afferent arterioles constrict. Neural Regulation  Kidneys are richly supplied by sympathetic fibers.  Strong stimulation (exercise or hemorrhage)–afferent arterioles are constricted.  Urine output is reduced, and more blood is available for other organs. Hormonal Regulation  Angiotensin II constricts afferents and efferents, diminishing GFR.  Atrial Natriuretic Peptide relaxes mesangial cells, increasing capillary surface area and GFR.  ANP is secreted in response to stretch of the cardiac atria. Tubular Reabsorption and Secretion  Much of the filtrate is reabsorbed by both active and passive processes.  Especially water, glucose, amino acids, and ions  Secretion helps to mange pH and rid the body of toxic and foreign substances. Reabsorption Routes  Paracellular Reabsorption- Passive fluid leakage between cells.  Transcellular Reabsorption- Directly through the tubule cells. Transport Mechanisms  Primary Active Transport- Uses ATP, like Na /K pumps & At rest, accounts for 6% total body ATP use.  Secondary Active Transport- Driven by ion’s electrochemical gradient, Symporters move substances in same direction, & Antiporters move substances in opposite directions. Water Reabsorption  Obligatory water reabsorption- 90% water follows the solutes that are reabsorbed.  Faculative water reabsorption- 10% regulated by ADH. Reabsorption in the Loop of Henle  Water reabsorption occurs in the descending limb.  The ascending limb is virtually impermeable to water.  Na - K - 2Cl symporters are present in the ascending limb.  Little obligatory water reabsorption occurs. Reabsorption in early DCT + –  Na - Cl symporters reabsorb ions.  PTH stimulates reabsorption of Ca2+.  It also inhibits phosphate reabsorption in the PCT, enhancing its excretion. Late DCT and Collecting Duct + + +  Principal Cells- Na -K pumps reabsorb Na & Aquaporin – 2 reabsorbs water. Stimulated by ADH.  Intercalated Cells- Reabsorb K + HCO , sec3ete H+. Urine Production  Fluid intake is highly variable.  Homeostasis requires maintenance of fluid volumes within specific limits.  Urine concentration varies with ADH.  High intake – Dilute urine of high volume.  Low intake – Concentrated urine of low volume. Formation of Dilute Urine  Glomerular filtrate and blood have the same osmolarity – 300mOsm/Liter.  Tubular osmolarity changes due to a concentration gradient in the medulla.  When dilute urine is formed, osmolarity in the tubule: Increases in the descending limb, decreases in the ascending limb and more in the collecting duct. + + –,  Thick Ascending Limb- Symporters actively resorb Na , K , Cl , Low water permeability, & Solutes leave, water stays in tubule.  Collecting Duct- Low water permeability in absence of ADH. Formation of Concentrated Urine  Juxtamedullary Nephrons with long loops.  Osmotic gradient is created by the Countercurrent Multiplier.  Solutes pumped out of ascending limb, but water stays in tubule. In presence of ADH, collecting ducts become very permeable to water.  Tubular fluid there becomes very concentrated.  Movement of water also carries urea into the medulla, contributing to its osmolarity.  Medulla osmolarity is increased.  In presence of ADH, collecting ducts become very permeable to water.  Tubular fluid there becomes very concentrated.  Movement of water also carries urea into the medulla, contributing to its osmolarity. Countercurrent Exchange  Loop and duct cells require nutrients and oxygen from blood supply.  Capillaries that feed them (vasa recta) form loops like those of nephron loops in the medulla.  Incoming and outgoing blood will have similar osmolarity.  This maintains medulla concentration gradient. Evaluation of Kidney Function  Routine urinalysis primarily evaluates for the presence of abnormalities in the urine: Albumin, Glucose, RBC, Ketone bodies, & Microbes. Urine Transport Storage  Each ureter transports urine from a renal pelvis by peristaltic waves, hydrostatic pressure, and gravity.  No anatomical valve at the opening of the ureter into bladder – when bladder fills, it compresses the opening and prevents backflow.  The bladder is a hollow, distensible, muscular organ with a capacity averaging 700–800 mL. Micturition  The discharge of urine involves voluntary and involuntary muscle contractions.  Stretch receptors trigger a spinal reflex, which we learn to control in childhood.  The urethra carries urine from the internal urethral orifice to the exterior of the body.  In males, it discharges semen as well as urine.


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