Transcript kidneys - Learning Central

The Kidney and formation
of urine
Objectives
• State the main functions of the kidney
• Label a diagram to illustrate the location of the kidneys,
ureters and bladder within the body
• Label a diagram of the kidney (to illustrate the renal cortex,
renal medulla, renal pyramid, renal pelvis, major and minor
calyces, renal artery and vein and the ureter)
• Label a diagram of a nephron (to illustrate the afferent and
efferent arteriole, glomerulus, glomerular capsule, proximal
convoluted tubule, loop of Henle, distal convoluted tubule,
and collecting duct)
Objectives
• List and briefly explain the three stages in the process of
urine formation
• State the main role of ADH and aldosterone in the
formation of urine
• List the main constituents of normal urine
• State the average urine output daily
• Briefly discuss the importance of the kidney in relation to
homeostasis
Main function of the Kidney
• The main function of the urinary system is: Elimination of
water-soluble substances
• Each day the kidneys filter >150L of fluid from the blood
plasma
• Most of this fluid (containing vital constituents such as
electrolytes, nutrients and water) is recovered by the
kidneys and returned to the blood
• This leaves only 1 - 2L of fluid (containing water soluble
waste) to be excreted as urine
There are 2 kidneys,
situated at the back of the abdomen
The kidneys and homeostasis
The kidneys are regulatory organs that function
to maintain a normal body state under
variations in the environment (homeostasis)
Which of the graphs best represents
homeostasis?
The Nephron
• Functional unit of the kidney is the nephron (about
one million nephrons in each kidney)
Formation of Urine
Three Phases:1. Glomerular Filtration
2. Selective Reabsorption
3. Secretion
Glomerular Filtration
What you think will
happen to water and
other small (water
soluble) molecules
such as glucose,
water, salts, urea?
Answer: They will be
forced into
glomerular capsule
Glomerular Filtration
What will happen to
large molecules
(such as blood cells
and plasma
proteins)?
Answer: They will
remain in the
capillary
Glomerular Filtration
good blood flow
high capillary pressures
Capillary wall
Capsule wall
Fluid in here = FILTRATE
Tubule
Peritubular capillary
Reabsorption
An extensive network of capillaries around the renal
tubules provides a large surface area for contact
Reabsorption
How essential substances are recovered by the
body (and not lost in the urine) = Reabsorption
This will be achieved by re-absorption (or not) of
constituents from the filtrate in the tubules to
the blood in the peri-tubular capillaries
Purpose of re-absorption is to reabsorb filtrate
constituents needed by the body to maintain
fluid and electrolyte balance and blood
alkalinity
Formation of Urine: Re-absorption
Peritubular capillary
Tubule
The function of reabsorption is to:
•Retain substances
that are needed by the
body
•E.g. glucose, amino
acids, water, salts
Reabsorption
What of the substances in the Filtrate would the
body want to recover:
• Completely?
• Partially?
• Not at all?
Reabsorption
Complete reabsorption
• Some constituents of the GF are completely
reabsorbed (actively) unless present in
excessive quantities
• This is because they are needed by the body
e.g. glucose 100% absorbed
Reabsorption
Partial Reabsorption
• The re-absorption of some substances
varies according to the need e.g. Water
and salts
• Anti Diuretic Hormone (ADH) regulates
the amount of water reabsorbed by the
kidney
Reabsorption
Increased blood concentration 
Detected by hypothalamus 
Secretion of ADH 
ADH released by the pituitary 
More water reabsorbed 
Decreased urine output and
Decreased blood concentration
Reabsorption
Partial Reabsorption
• The hormone aldosterone increases reabsorption of sodium by the kidney (water
follows)
• This will lead to a decreased urine output
Reabsorption
No reabsorption
• Waste products are absorbed only to a slight
extent (e.g. UREA) or not at all (e.g.
CREATININE)
• Urea is the chief nitrogenous waste of
mammals.
• Creatinine is a break-down product of
creatine phosphate in muscle, and is usually
produced at a fairly constant rate by the body.
The urea cycle
Breakdown of amino acids (deamination) 
Ammonia
Ammonia is extremely toxic!
The liver contains enzymes
which quickly converts the
ammonia into urea.
(less toxic than ammonia)
Urea is removed efficiently by the KIDNEYS
Recap – Filtration and Reabsorption
Secretion
How excess waste (and / or toxic substances) is
removed from the blood and added to the
urine = Secretion
Addition of substances from the blood stream
to the filtrate e.g. some drugs and H+ ions
Functions of secretion is to eliminate waste and
maintain blood pH
Formation of Urine: Secretion
Tubule
Peritubular
capillary
Toxins, Drugs,
Waste, H+
The function of secretion is to:
* Remove substances that are
toxic
* Maintain acid-base balance
Secretion is the opposite
of re-absorption
Filtrate Urine  Bladder
Filtration, Reabsorption, Secretion
Normal amounts and constituents of urine
H2O
1 - 2 L/day - average
?? mls/day – minimum
30 – 40 mls/hr - minimum
Urea
Creatinine
Uric acid
Na+, K+, Mg++
Formation of Urine: Filtration
Blood cells
Glomerular blood
Plasma proteins
Small molecules
Capillary wall
Capsule wall
Fluid in here = FLTRATE
Tubule
Peritubular capillary
Formation of Urine: Re-absorption
Tubule
Peritubular capillary
The function of reabsorption is to:
•Retain substances that
are needed by the body
•E.g. glucose, amino
acids, water, salts
Formation of Urine: Secretion
Tubule
Peritubular
capillary
Toxins, Drugs,
Waste, H+
The function of secretion is to:
* Remove substances that are
toxic
* Maintain acid-base balance
Secretion is the opposite
of re-absorption
Filtrate Urine  Bladder
Elimination of Urine: Micturition
Kidneys
Ureters
Bladder
Urethra
Case Study 1
• Callum is 12 months old and has been having very
loose stools for a couple of days.
• What effect is this likely to have on his fluid
balance?
• What mechanisms should enable homeostasis to be
maintained?
• What advice would you give his mother?
Case Study 2
• Stephen is 21 years old and has been drinking excessive
amounts of alcohol!
• How does alcohol effect his fluid balance?
• What advice would you give him to maintain homeostasis
and health?
• What problems might you encounter in giving such advice?
• What strategies are in place to reduce the amount of
alcohol consumed by young people?
Case Study 3
• Sarah has been taking Clozapine to control the symptoms of her
schizophrenia.
• Her CPN visits her and she confides in him that her housemates are
stealing her possessions during the night and have also been trying to
poison her.
• She has started locking her door and is refusing to eat anything unless
it is sealed and she has bought it herself from the local shop.
• The CPN suspects that Sarah has been taking cannabis (she has a
history of drug abuse).
• How might the mental health team establish if Sarah is experiencing
drug induced psychosis?
• What other possible explanations are there for this situation?
Case Study 4
• Caroline is 29 and expecting twins. She is 30 weeks
into her pregnancy.
• She visits the clinic for a routine assessment.
• The nurse does a urine tests and finds that there is
protein present in Caroline’s sample.
• Should there be protein in Caroline’s urine?
• If not, why not?
• Does this indicate a problem with Caroline’s
kidneys?
• Where else might the protein have come from?
Case Study 5
• Mrs Evans (who is 65 years of age) has Non Insulin
Dependent Diabetes Mellitus (NIDDM).
• She regularly tests her blood glucose levels.
• This morning, after breakfast, it was 9mmol/L.
• Would you expect her urine to contain glucose?
(explain your answer)
• After lunch it was 12mmol/L.
• Now would you expect her urine to contain
glucose? (explain your answer).
• What are the implications in terms of urine testing
for people with diabetes?