Transcript The Urinary System

The Urinary System
Mr O. Tada
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Introduction
Functions
Gross structure & function
Micro-structure of Kidney (Nephron)
Urine formation
Hormones & Kidney function
Micturition
Maintenance of Acid-Base balance
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Functions
Produces Urine (formed from blood)
Maintain volume of extracellular fluid
Maintain ionic balance in extracellular fluid
Maintain pH and osmotic concentration of the
extracellular fluid
Excrete toxic metabolic by-products such as
urea, ammonia, and uric acid
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Structure & Function
Kidney
Pair of Organs
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Bean-Shaped--Most Species
Heart-Shaped—Horses
Lobulated—Cattle
Blood Supply

Renal Artery
 Brings blood to Kidney
 Arises directly from aorta

Renal Vein
 Brings blood away from Kidney
 Empties into the Caudal Vena Cava
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Divisions

Cortex
 Outer Portion
 Contains upper parts of nephrons (Glomeruli and
Tubules)

Medulla
 Inner Portion
 Contains lower parts of nephrons (Loops of Henle and
Collecting Ducts)
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Renal Pelvis -Drains kidney and connects ureters
Renal Hilus
 Indented area on concave edge
 Ureter, Blood Vessels, Nerves and Lymphatics enter or
leave
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Structure & Function
Ureter
Smooth muscle lined tube
Conveys urine from renal pelvis to bladder
Enter bladder through uretero-vesicular junction
 Acts as a valve
 Prevents backflow
Urinary Bladder
Hollow muscular organ (Smooth Muscle)
Stores Urine (Stretches)
Lined with Transitional Epithelium
 Flatten when filling occurs
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Structure & Function
Urethra
Caudal continuation of the neck of the
bladder
Conveys urine from bladder to exterior
Urine release into urethra controlled by
external sphincter
 Skeletal muscle
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All in one!
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Micro-structure of Kidney (Nephron)
The functional unit of the kidney


Numbers range from 250,000 (cat) to 4
million (cow) per kidney
Components
 i. Glomerulus
 ii. Bowman's Capsule
 iii. Proximal Tubules
 iv. Loop of Henle
 v. Distal Tubules
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This is it!!!
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Nephron > Glomerulus
Tufts of Capillaries
Afferent arterioles
 Conduct blood to glomerulus
Efferent arterioles
 Conduct blood away from glomerulus
Function:
 Filtration of Blood
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Nephron > Capsule & Prox
tubule
Bowman's Capsule


a. Collect Glomerular Filtrate
b. Conduct filtrate into proximal tubules
Proximal Tubules
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a. Conduct filtrate into Loop of Henle
b. Very convoluted (Surrounded by
Peritubular Capillaries)
c. Reabsorb, Secrete, & Excrete
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Nephron > Loop of Henle
Play important role in concentration of
urine
Divisions

Descending limb
 thin segment
 simple squamous epithelium

Ascending limb
 thick segments
 simple cuboidal epithelium
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Nephron > Distal & J. App
Distal tubules
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a. Convey urine from Loops of Henle
b. Also convoluted (Surrounded by peritubular
capillaries)
c. Reabsorb, Secrete, and Excrete
d. Feed Collecting tubules and ducts
Juxtaglomerular Apparatus
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a. Junction between distal tube and glomerulus
b. Contain unique cell types
 i. Macula Densa in tubules
 ii. Juxtaglomerular cells in arterioles
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Nephron cont’d

c. Function:
 i. Regulate renal blood flow
 ii. Regulate glomerular filtration
 iii. Secrete Renin

--Involved in production of angiotensin II
Two Types of Nephrons

a. Cortical
 i. Short loops of Henle
 ii. Only go into Outer medulla

b. Juxtamedullary
 i. Long loops of Henle
 ii. Can go clear to renal pelvis
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Principal roles of Nephron
Glomerular filtration
of water and solutes
from the blood
Tubular reabsorption
of water and
conserved molecules
back into the blood
Tubular secretion of
ions and other waste
products from
surrounding capillaries
into the distal tubule
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Urine Formation
Filtration in the glomerulus and nephron
capsule
Re-absorption in the proximal tubule
Tubular secretion in the Loop of Henle
!!!More details coming NOW!!!
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Glomerular Filtration
Glomerulus favors filtration
Peritubular capillaries favor reabsorption
Slit pores at glomerulus filter larger molecules
Macula densa sensitive to changes in ionic
concentrations (Na+ and Cl-)
Juxtaglomerular cells secrete Renin and
initiates Angiotensin II

Increases water reabsorption by tubules to
peritubular capillaries
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Tubular Re-absorption & Secretion
Re-absorption Path
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a. Tubular Lumen
b. Tubular Epithelium
c. Interstitial Fluid
d. Capillary
Secretion Path

Just the opposite
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Re-absorbed Molecules
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a. Amino Acids & Glucose
b. Use carrier proteins coupled with Na+ to enter
tubular cells
c. Water reabsorption follows osmotic gradient
from lumen to epithelium to capillaries
d. Other diffusible substances follow water by
diffusion because they increase in concentration in
the lumen
 --Proximal Tubule Reabsorption (65% of H2O, Na+, Cl-,
and 100% of Glucose and Amino Acids)
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Secreted Molecules
a. H+ is secreted throughout tubules
 b. K+ is secreted in distal and collecting tubules
 c. Ammonia is secreted
 --Depends on acid-base balance
Species differences:
 a. Desert Kangaroo Rat
 i. Only long loops of Henle
 ii. Can live on Metabolic H2O
 b. Humans, Cattle, & Swine
 i. Few long loops (1/3 to 1/5 of total)
 ii. Void large amounts of dilute urine
 c. Dogs, Cats, Camels, Sheep, and Goats
 i. Many long loops of Henle
 ii. Produce relatively concentrated urine
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Hormones in the Kidney
Antidiuretic Hormone/Vasopressin
 Synthesized by hypothalamus, secreted by posterior
pituitary (or neurohypophysis)
 Low Blood [ADH] = increased H20 excretion or a dilute
urine
 High Blood [ADH] = increased solute excretion or a
concentrated urine

ADH allows H2O reabsorption by late distal tubules and
collecting ducts thus facilitating the concentration of urine
 ADH facilitating the formation of "water channels" on the
luminal membrane of tubule and ductal epithelial cells
 ADH also increases the permeability of the collecting ducts
to urea
 ADH decrease blood flow of the vasa recta
 Without ADH the late distal tubules and collecting ducts
nephron are impermeable to H2O
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Angiotensin II
Causes Efferent arteriole to constrict

Increases GFR
Increases water reabsorption by tubules
to peritubular capillaries
Increases vasoconstriction of peripheral
blood vessels
Causes the secretion of Aldosterone
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Aldosterone
Produced in adrenal cortex (Mineralocorticoid)
Involved in K+ regulation
Causes secretion in distal tubules, collecting
tubules and ducts
Causes H2O reabsorption (increase blood
volume & pressure)
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Parathyroid Hormone
Causes a reabsorption of Ca++
Secretion of Phosphorus
Controls formation of Vitamin D
Activated in kidney
Vitamin D promotes Ca++ absorption
from intestine
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Micturition (Urinating)
Transfer of Urine to the Urinary Bladder
From Glomerulus to Renal Pelvis
(hydrostatic pressure)
From Renal Pelvis to Bladder (peristalsis of
the ureter)
Micturition Reflexes
Micturition: Emptying of Bladder
Involuntary or Voluntary Control
Sympathetic Control --closure of sphincter
during ejaculation
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Acid-Base Balance
Relationship of pH to H+ Concentration
Normal = pH 7.4
Severe Acidosis = pH 7.
a. H+ concentration doubled
Severe Alkalosis = pH 7.7
 H+ concentration halved
Mechanism of H+ Secretion by the Kidneys
Na+/H+ antiporter secretes H+
 a. Occurs along whole nephron
 b. 85% in Proximal tubules
Secreted H+ combines with: Bicarbonate, Phosphate,
Ammonia
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Role of Respiratory System
Respiratory System also controls pH of extracellular
fluids
Bicarbonate from hydration reaction binds CO2
Releases H+ with CO2 at alveoli
Increased H+ and CO2 in extracellular fluid cause
increase ventilation
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Chemical Buffer Systems and Mechanisms
System can buffer acids and bases in extra-cellular fluids
Bicarbonate
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Acid buffer:
 HCl + NaHCO3 --> H2CO3 + NaCl
Base buffer:
 NaOH + H2CO3 --> NaHCO3 + H2O
Phosphate
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Acid buffer:
 HCl + Na2HPO4 --> NaH2PO4 + NaCl
Base buffer:
 NaOH + NaH2PO4 --> Na2HPO4 + H2O
Proteins
 i. Amino-end (basic) buffer acids
 ii. Carboxy-end (acidic) buffer bases
 iii. Hemoglobin most abundant buffer in body
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