Composition and Functions of Urine

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Questions and Answers

What is the daily production range of urine?

1000ml-1500ml

What is the specific gravity range of urine?

1020-1030

What is the main function of the Renin Angiotensin Aldosterone System (RAAS)?

Regulate electrolyte balance and blood pressure

What stimulates the release of Antidiuretic Hormone (ADH) to increase water reabsorption?

Increased blood osmotic pressure Signup and view all the answers

What is the smallest volume of urine required daily to excrete waste products?

500ml/day Signup and view all the answers

What is the main component of urine in terms of percentage?

Water (96%) Signup and view all the answers

Which hormone increases water reabsorption by increasing the permeability of the distal convoluted tubule and collecting ducts?

ADH Signup and view all the answers

What is the hormone responsible for increasing reabsorption of sodium and water and excretion of potassium?

Aldosterone Signup and view all the answers

Name the hormone that increases the reabsorption of sodium and water from the proximal convoluted tubule and collecting duct.

ANP (Atrial Natriuretic Peptide) Signup and view all the answers

What is the function of Calcitonin in the body related to blood calcium levels?

Lowers the blood calcium level Signup and view all the answers

Which hormone helps in increasing blood calcium levels?

Parathyroid hormone Signup and view all the answers

What is the main function of the proximal convoluted tubule in the formation of urine?

Reabsorption of water, glucose, amino acids, sodium, bicarbonate, chloride, and potassium Signup and view all the answers

What is the significance of Loop of Henle in the urine formation process?

Creates a gradient of increasing Na ion concentration towards the end of the loop within the interstitial fluid of the renal pyramid Signup and view all the answers

How does the distal convoluted tubule regulate pH in the blood?

By secreting H⁺ when the pH of the plasma is low Signup and view all the answers

What is the main role of the collecting duct in the urinary system?

Allows for the osmotic reabsorption of water Signup and view all the answers

In which part of the nephron does most reabsorption of essential substances occur?

Proximal convoluted tubule Signup and view all the answers

What happens to the glomerular filtration rate (GFR) when blood pressure rises?

GFR reduces Signup and view all the answers

Study Notes

Urine Composition

Urine is a liquid by-product with a clear and amber color (pigmented urobilin)
Specific gravity of urine is 1020-1030
pH of urine is 4.5-8
Daily production of urine is 1000ml-1500ml
Composition of urine includes:
- Water (96%)
- Urea (2%)
- Uric acid
- Creatinine
- Ammonia
- Sodium
- Potassium
- Chlorides
- Phosphates
- Sulphates
- Oxalates

Water Balance and Urine Output

Balance between fluid intake and output is controlled by kidneys
Smallest volume required to excrete waste products is 500ml/day
More than 500ml of urine production is controlled by ADH (Antidiuretic Hormone)
Increased blood osmotic pressure stimulates osmoreceptors, which stimulate posterior pituitary and release ADH, reducing blood osmotic pressure
ADH increases water reabsorption
Increased blood volume stimulates stretch receptors in the heart, releasing ANP (Atrial Natriuretic Peptide), which reduces the reabsorption of water and sodium and inhibits ADH secretion

RAAS (Renin-Angiotensin-Aldosterone System)

RAAS regulates electrolyte balance and blood pressure
Low renal blood flow due to low blood volume, low blood pressure, or low blood sodium triggers the secretion of Renin from kidneys
Renin converts Angiotensinogen to Angiotensin I, which is then converted to Angiotensin II by ACE
Angiotensin II increases blood pressure through vasoconstriction
Angiotensin II also stimulates the secretion of Aldosterone from the adrenal cortex
Aldosterone increases sodium and water reabsorption, increases potassium excretion, and increases blood sodium and blood volume, leading to an increase in blood pressure

Urine Flow Pathway

Urine flows through the following pathway:
- Distal convoluted tubules
- Collecting ducts
- Large papillary ducts
- Renal pelvis
- Major calyces
- Minor calyces

Hormonal Influence on Urine Formation

Parathyroid hormone increases blood calcium levels
Calcitonin lowers blood calcium levels
ADH increases water reabsorption by increasing the permeability of distal convoluted tubules and collecting ducts
Aldosterone increases the reabsorption of sodium and water and excretion of potassium
ANP (Atrial Natriuretic Peptide) increases the reabsorption of sodium and water from proximal convoluted tubules and collecting ducts

Formation of Urine

3 processes occur in the formation of urine:
- Filtration
- Reabsorption
- Secretion
Reabsorption:
- Occurs mainly in the proximal convoluted tubule
- Reabsorbs water, glucose, amino acids, sodium, and other substances
- Epithelial lining has microvilli to increase surface area
Proximal Convoluted Tubule:
- Reabsorbs 65% of Na+, 65% of H2O, 90% of filtered bicarbonate, 50% of Cl- and K+
Loop of Henle:
- Creates a gradient of increasing Na ion concentration towards the end of the loop within the interstitial fluid of the renal pyramid
- Reabsorbs 25% of Na+, 15% of water, and 40% of K+
Distal Convoluted Tubule:
- Under the influence of Aldosterone, reabsorbs Na⁺ and secretes K⁺
- Regulates pH by secreting H⁺ when pH of the plasma is low
- Only 10% of the filtered NaCl and 20% of water remains
Collecting Duct:
- Allows for the osmotic reabsorption of water

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Description

Learn about the composition and key functions of urine, including pH level, specific gravity, and daily production. Explore the substances that make up urine and their percentages. Understand the importance of water balance and urine output.