The Kidney and formation of urine. Objectives State the main functions of the kidney Label a diagram...
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Transcript of The Kidney and formation of urine. Objectives State the main functions of the kidney Label a diagram...
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, There are 2 kidneys,
situated at the back of the abdomensituated at the back of the abdomen
The kidneys and homeostasisThe 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
Capillary wall
Capsule wall
Tubule Peritubular capillary
Fluid in here = FILTRATE
good blood flowgood blood flow
high capillary pressureshigh capillary pressures
Reabsorption
An extensive network of capillaries around the renal An extensive network of capillaries around the renal tubulestubules provides a provides a large surface arealarge surface area for contact for contact
ReabsorptionHow 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
TubuleThe function of re-absorption 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
ReabsorptionIncreased 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 re-
absorption of sodium by the kidney (water follows)
• This will lead to a decreased urine output
ReabsorptionNo 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 cycleBreakdown of amino acids (deamination)
AmmoniaAmmonia 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: SecretionPeritubular capillary
Toxins, Drugs, Waste, H+Tubule
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 urineH2O 1 - 2 L/day - average
?? mls/day – minimum30 – 40 mls/hr - minimum
Urea
Creatinine
Uric acid
Na+, K+, Mg++
Formation of Urine: Filtration
Blood cells
Plasma proteins
Small molecules
Glomerular blood
Capillary wallCapsule wall
TubulePeritubular capillary
Fluid in here = FLTRATE
Formation of Urine: Re-absorption
Peritubular capillary Tubule
The function of re-absorption is to:
•Retain substances that are needed by the body
•E.g. glucose, amino acids, water, salts
Formation of Urine: SecretionPeritubular capillary
Toxins, Drugs, Waste, H+Tubule
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: MicturitionKidneys
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?