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Excretion

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Renal Corpuscle Anatomy ---Bowman's capsule -Glomerulus -PCT. Afferent arteriole ... Dilation of afferent arteriole or constriction of efferent arteriole increases GFR ... – PowerPoint PPT presentation

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Title: Excretion


1
Excretion
  • Anatomy and Physiology of the Urinary System

2
Excretion Defined
  • Elimination of metabolic wastes

3
Systems Involved in Excretion
  • Urinary system
  • _____
  • Respiratory system
  • ____________
  • Digestive system
  • _____
  • Integumentary system
  • _____

Urine
Carbon dioxide
Feces
Sweat
4
Functions of the Urinary System
  • Excretion of metabolic wastes
  • Regulates fluid and electrolyte balance
  • Regulates blood pH
  • Produces hormones
  • Calcitriol (vitamin D) helps regulate calcium
  • Erythropoietin regulates RBC formation
  • Regulates blood pressure by enzyme renin

5
Anatomy of the urinary system
  • Kidneys filter blood and produce urine
  • Ureters transport urine to urinary bladder
  • Urinary bladder stores urine until eliminated
  • Urethra is tube for elimination of urine

Kidney-----
Ureter----------
Urinary bladder----------
Urethra----------------------
6
Kidney Anatomy
  • Renal capsule sheaths kidney
  • Renal cortex is outer region
  • Renal medulla is inner region with 8-18 renal
    pyramids
  • Renal papilla is apex or tip of renal
    pyramid
  • Renal columns are cortical tissue between
    pyramids

Renal capsule-----
Renal papilla------
Renal cortex-----
Renal pyramid--------
Renal column---------------
7
Anatomy of Kidney Continued
  • Minor calyx receives urine from renal papilla
  • Major calyx collects urine from two or more minor
    calyces
  • Renal pelvis collects urine from all calyces
  • Ureter carries urine to bladder

---------------Minor calyx
Major calyx---------
Renal pelvis--------------
---Ureter
8
Nephron
  • Microscopic filtering units of kidneys composed
    of renal tubules and a blood supply
  • Called functional units make most of urine
  • About 1.25 million per kidney
  • Mostly in renal cortex with some tubules
    extending into renal pyramids of medulla

9
Nephron Continued
  • Structure
  • Renal corpuscle
  • Loops of capillaries called glomerulus
  • Double layered Bowmans capsule surrounds
    glomerulus
  • Renal tubules
  • Proximal convoluted tubule (PCT) connects to
    Bowmans capsule
  • Loop of Henle with descending and ascending limbs
  • Distal convoluted tubule (DCT) is last part of
    nephron
  • DCT of several nephrons connect to a collecting
    duct (CD)

10
Nephron Anatomy
Bowmans capsule----------------
-------------Glomerulus
PCT------------------------------
----------DCT
Descending limb of Henle----------------
-----------Ascending limb of Henle
---------CD
11
Renal Corpuscle Anatomy
---Bowmans capsule
Afferent arteriole----------
-------Glomerulus
DCT-----------------
-------PCT
Efferent arteriole-----
--------Capsular space
12
Nephron Blood Supply
Peritubular capillaries----------------
-------Efferent arteriole
-------Afferent arteriole
----------------Vasa recta
13
Physiology of the Urinary System
  • Three processes required for urine formation

1. Filtration from the glomerulus to Bowman's
capsule
2. Tubular reabsorption from renal tubules to
blood
3. Tubular secretion from blood into the renal
tubules
Urine
1
2
3
14
Filtration
  • Water and many different solutes pass from
    glomerulus to the Bowmans capsule
  • Resulting fluid in capsular space called filtrate
  • Filtrate contains
  • Wastes such as urea and uric acid that must be
    eliminated in the urine
  • Useful (vital) substances such as water, organic
    nutrients and electrolytes that must be kept

15
Filtrate Formation
  • High glomerular blood hydrostatic pressure of
    about 55 mmHg forces water and solutes through
    filtration membrane
  • Formed by glomerular capillaries and visceral
    layer of Bowmans capsule

16
Filtration Continued
  • Amount of blood flow through kidneys in one
    minute renal blood flow (RBF)
  • About 1200 mL/minute
  • Amount of filtrate formed in one minute
    glomerular filtration rate (GFR)
  • Between 105 and 125 mL/minute
  • So around 10 of RBF becomes filtrate

17
Regulation of GFR How to keep GFR in
homeostasis as BP changes
  • Regulation by controlling glomerular blood flow
  • Dilation of afferent arteriole or constriction of
    efferent arteriole increases GFR
  • Increased blood flow in glomerulus causes
    increased filtration
  • Constriction of afferent arteriole or dilation of
    efferent arteriole decreases GFR
  • Decreased blood flow in glomerulus causes
    decreased filtration

18
Three Methods of Regulation
  • Autoregulation
  • Regulation of GFR by kidneys themselves
  • Neural regulation
  • Autonomic nervous system affects GFR
  • Hormonal regulation
  • Hormones indirectly affect GFR
  • All make adjustments in glomerular blood pressure

19
Tubular Reabsorption
  • Most of filtrate moves from the nephron tubules
    back into the blood
  • Water, organic nutrients and electrolytes are
    kept
  • Wastes leave with urine
  • Most reabsorption in proximal convoluted tubule

Blood of peritubular capillaries
20
Tubular Reabsorption Continued
  • Water reabsorbed by osmosis
  • Solutes reabsorbed by diffusion, active
    transport, cotransport, countertransport and
    pinocytosis

21
Reabsorption Continued
  • Most actively transported substances have a
    transport maximum (Tm)
  • The Tm refers to how many milligrams of a
    substance the nephron tubules can reabsorb in a
    minute
  • When Tm exceeded, substance shows up in urine
  • Renal threshold is the maximum blood
    concentration at which a substance begins to
    appears in the urine
  • Renal threshold for glucose 180 milligrams per
    100 mL (deciliter)

22
Tubular Secretion
  • Some solutes move from the blood of the nephron
    capillaries into the filtrate
  • Potassium, ammonium, hydrogen ions and
    bicarbonate ions are secreted into filtrate
  • Helps regulate acid-base balance and electrolyte
    concentrations

Blood of peritubular capillaries
23
Water Reabsorption
  • Each day we lose about as much water as we gain
  • If loss exceeds gain, become dehydrated
  • If gain exceeds loss, become over-hydrated
  • Controlled by reabsorption of varying amounts of
    water

24
Water Reabsorption Continued
  • Each day, between 150-180 L of filtrate
  • Each day, 1-2 L of urine
  • What does this tell you?
  • Amounts of H2O reabsorbed
  • 65 in proximal convoluted tubules
  • 15 in descending limbs of Henle
  • None in ascending limb of Henle
  • 10-15 in distal convoluted tubules
  • Remainder in collecting ducts

25
Types of Water Reabsorption
  • Obligatory water reabsorption
  • In PCT and descending LOH
  • More constant
  • Facultative water reabsorption
  • In DCT and CD
  • Variable, depending on degree of hydration
  • This reabsorption controlled by hormones

26
Setting Stage for Water Reabsorption
  • Remember, 65 of water that is reabsorbed is
    reabsorbed in the PCT
  • 15 is reabsorbed in descending LOH
  • Water not reabsorbed by ascending LOH
  • Salt (sodium chloride) is actively reabsorbed by
    ascending LOH
  • Filtrate becomes about 4X as concentrated at
    bottom of LOH lot more salt and urea at bottom

27
Water Reabsorption Continued
H2O-65
Less salt and urea
H2O-15
ISF and Blood
Urea
More salt and urea
28
Steps in Concentration of Urine
  • 1. As water loss exceeds gain, hypothalamus
    stimulates secretion of antidiuretic hormone
    (ADH) from the posterior pituitary
  • 2. ADH makes the cells of the DCT and CD more
    permeable to water adds water pores
  • 3. More water leaves the DCT and CD and enters
    concentrated interstitial fluid and blood of the
    pyramid

29
Steps in Concentration of Urine
  • 4. Concentrated interstitial fluid and blood take
    more water out of the filtrate and concentrate
    the urine
  • 5. Result is less of a dark, and concentrated
    urine
  • Aldosterone from adrenal cortex increases salt
    reabsorption from tubules and thus helps to
    concentrate urine
  • How does this work?

30
Concentration of Urine-ADH Present
ADH
DCT and CD more permeable to water and more water
reabsorbed
31
Steps in Dilution of Urine
  • 1. As water gain exceeds loss, hypothalamus stops
    secreting ADH
  • DCT and CD become less permeable to water water
    pores decrease
  • Less water is reabsorbed
  • More water stays in filtrate and urine

32
Steps in Dilution of Urine
  • 5. Results in more of a dilute urine
  • 6. Adrenal cortex decreases aldosterone
    secretion, thus less salt is reabsorbed from
    tubules and this helps to dilute urine

33
Dilution of Urine
No ADH, so DCT and CD less permeable to water and
less water reabsorbed
34
Urine the final product
  • Urine composition
  • 95 H2O
  • 5 solutes (solids)
  • Electrolytes
  • Nitrogenous wastes such as urea, creatinine and
    uric acid
  • Urea from __________________
  • Creatinine from ________________
  • Uric acid from ____________________

protein metabolism
muscle metabolism
nucleic acid metabolism
35
Urine Continued
  • Characteristics of Urine
  • Color
  • Turbidity
  • Specific gravity
  • pH

36
Clinical Terms
  • Glomerulonephritis
  • Acute and Chronic Renal failure
  •  
  • Hemodialysis (kidney dialysis)
  • Renal Calculi
  •  

37
Polycystic Disease
  • Incurable, kidney disease in which cysts form in
    kidney, and destroy it. Cysts can be clearly seen
    in kidney below it weighed 17 pounds.

Cyst-------------
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