Title: Excretion
1Excretion
- Anatomy and Physiology of the Urinary System
2Excretion Defined
- Elimination of metabolic wastes
3Systems Involved in Excretion
- Urinary system
- _____
- Respiratory system
- ____________
- Digestive system
- _____
- Integumentary system
- _____
Urine
Carbon dioxide
Feces
Sweat
4Functions 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
5Anatomy 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----------------------
6Kidney 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---------------
7Anatomy 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
8Nephron
- 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
9Nephron 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)
10Nephron Anatomy
Bowmans capsule----------------
-------------Glomerulus
PCT------------------------------
----------DCT
Descending limb of Henle----------------
-----------Ascending limb of Henle
---------CD
11Renal Corpuscle Anatomy
---Bowmans capsule
Afferent arteriole----------
-------Glomerulus
DCT-----------------
-------PCT
Efferent arteriole-----
--------Capsular space
12Nephron Blood Supply
Peritubular capillaries----------------
-------Efferent arteriole
-------Afferent arteriole
----------------Vasa recta
13Physiology 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
14Filtration
- 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
15Filtrate 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
16Filtration 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
17Regulation 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
18Three 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
19Tubular 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
20Tubular Reabsorption Continued
- Water reabsorbed by osmosis
- Solutes reabsorbed by diffusion, active
transport, cotransport, countertransport and
pinocytosis
21Reabsorption 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)
22Tubular 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
23Water 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
24Water 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
25Types 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
26Setting 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
27Water Reabsorption Continued
H2O-65
Less salt and urea
H2O-15
ISF and Blood
Urea
More salt and urea
28Steps 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
29Steps 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?
30Concentration of Urine-ADH Present
ADH
DCT and CD more permeable to water and more water
reabsorbed
31Steps 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
32Steps 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
33Dilution of Urine
No ADH, so DCT and CD less permeable to water and
less water reabsorbed
34Urine 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
35Urine Continued
- Characteristics of Urine
- Color
- Turbidity
- Specific gravity
- pH
36Clinical Terms
- Glomerulonephritis
- Acute and Chronic Renal failure
-
- Hemodialysis (kidney dialysis)
- Renal Calculi
-
-
37Polycystic 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-------------