Human Physiology Week 7

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Questions and Answers

Which statement accurately describes the function of nephrons?

They regulate heart rates.

They primarily produce blood cells.

They transport blood to the heart.

They filter fluids and produce urine. (correct)

The renal pelvis is where all fluid from the major calyxes is drained into.

True

What hormone is secreted by the adrenal glands to help retain more sodium in the kidneys?

Aldosterone

The ______ tubule is located closest to the glomerulus.

proximal convoluted Signup and view all the answers

Match the renal processes with their descriptions:

Diuresis = Filtering water from plasma into urine Natriuresis = Removing sodium from the bloodstream Glomerular filtration = Initial process of filtering blood into Bowman’s capsule Reabsorption = Returning substances from filtrate back into the blood Signup and view all the answers

What is the effect of high sodium intake on blood pressure?

Increases osmolarity of extracellular fluid Signup and view all the answers

Chronic high salt meals improve the kidneys' ability to eliminate sodium.

False Signup and view all the answers

Define micturition.

The process of urination where the bladder contracts to expel urine. Signup and view all the answers

If pH becomes too acidic, hydrogen ions are pushed out quicker through ______ to maintain bicarbonate buffer.

urine Signup and view all the answers

Match the following kidney functions with their descriptions:

Acid-Base Balance = Elimination of excess hydrogen ions and reabsorption of bicarbonate Micturition Reflex = Involuntary and voluntary control of urination Sodium Retention = Increased fluid in the blood leading to higher blood pressure Diuretics = Medication that inhibits sodium reabsorption Signup and view all the answers

What primarily triggers thirst when sodium levels increase?

Osmoreceptors Signup and view all the answers

The external urethral sphincter is controlled involuntarily.

False Signup and view all the answers

What happens to the bladder during micturition?

The bladder contracts and decreases in size. Signup and view all the answers

The kidneys help maintain a basic pH of around ______.

7.4 Signup and view all the answers

Which statement about the sympathetic nervous system's effect on the bladder is correct?

It relaxes the bladder Signup and view all the answers

Study Notes

Kidney Anatomy

The kidneys are located in the abdomen and are retroperitoneal, meaning they are behind the peritoneal layer.
They are connected to the bladder via ureters.
A blockage in the ureter can cause fluid to back up.
Individuals with spinal cord injuries may experience issues controlling their bladder.

Kidney Layers

The cortex is the outer layer of the kidney.
The medulla is the inner layer of the kidney.
Renal pyramids are located within the medulla and contain nephrons, the functional units of the kidney.

Nephrons

Nephrons filter fluids and direct them into the papilla.
The glomerulus is a network of capillaries located in the nephron, where filtration occurs.
Minor calyxes collect fluid filtered from the nephrons.
Major calyxes collect fluid from multiple minor calyxes.
The renal pelvis collects fluid from all the major calyxes.

Renal Vasculature

Blood enters the kidney via the renal artery.
The renal artery branches into smaller arteries that follow the renal pyramids, known as interlobar arteries and veins.
These arteries further branch into arcuate arteries.
Interlobular arteries and veins are the next level of branching.
The interlobular arteries branch into afferent arterioles that supply the glomerulus.
Efferent arterioles carry blood away from the glomerulus.
Efferent arterioles branch into peritubular capillaries where reabsorption occurs.

Tubules

The tubules allow fluid to collect and eventually form urine.

Nephron Components

The glomerulus is the starting point of each nephron and is located in the cortex.
Each glomerulus is connected to a complex tubular system, forming the nephron.
As blood enters the afferent arteriole, it travels through the convoluted loop system.
Plasma filters out of the capillaries and into Bowman's space.
Proximal convoluted tubule is the first component of the tubular system following the glomerulus.
The proximal convoluted tubule transitions into the proximal straight tubule.
The thin descending limb and thin ascending limb together form the Loop of Henle.
The thick ascending limb connects to the distal convoluted tubule.
Multiple nephrons ultimately connect to collecting ducts, which empty into the renal calyx.
The collecting ducts empty into the papilla, where urine is formed.

Juxtamedullary Nephron

The juxtamedullary nephron has a glomerulus that is located near the medulla.
Peritubular capillaries surround the tubules in the cortex.

Renal Processing of Plasma

Molecules present in plasma as it passes through the glomerulus include electrolytes (potassium, sodium, calcium, phosphates), glucose, hormones, and drugs.
These molecules can be reabsorbed back into the peritubular capillaries, secreted into the tubular system, or excreted into the urine.

Renal Regulation of Water Balance

Volume expansion (hyperhydration) occurs when there is an abundance of fluid and blood travelling through the glomerulus, resulting in high capillary hydrostatic pressure. This leads to diluted filtrate and less fluid being reabsorbed, resulting in increased urine volume.
Volume contraction (dehydration) occurs when there is a low volume of blood in the peritubular capillaries, resulting in decreased capillary hydrostatic pressure and a concentrated filtrate. Increased colloid osmotic pressure pulls fluid from the lumen into the capillary, resulting in increased water reabsorption and decreased urine volume.

Water and Plasma Osmolarity

Hyperhydration leads to dilute blood and decreased plasma osmolarity, inhibiting osmoreceptors in the anterior hypothalamus and decreasing ADH secretion from the posterior pituitary. This results in less water reabsorption and more dilute urine.
Dehydration leads to concentrated blood and increased plasma osmolarity, stimulating osmoreceptors in the anterior hypothalamus. This triggers thirst, increases ADH secretion, and leads to increased water reabsorption and more concentrated urine.

Diuresis and Natriuresis

Diuresis refers to the removal of water from the body by filtering it from the plasma and excreting it as urine.
Natriuresis refers to the removal of sodium from the bloodstream by filtering it and excreting it as urine.
Increased arterial blood pressure leads to greater pressure in the afferent arterioles and glomerular capillaries, resulting in increased capillary hydrostatic pressure. This increased pressure pushes more fluid and sodium into Bowman's capsule.

Renin-Angiotensin-Aldosterone System (RAAS)

The RAAS helps regulate arterial blood pressure and is activated under three primary conditions:
- Decreased arterial blood pressure:
  - Juxtaglomerular cells in the juxtaglomerular apparatus sense decreased blood pressure.
  - They secrete the hormone renin, which activates angiotensinogen (from liver) to form angiotensin I.
  - Angiotensin converting enzyme (ACE) in the lungs modifies angiotensin I into angiotensin II.
  - Angiotensin II causes vasoconstriction (increased TPR) and stimulates the adrenal glands to release aldosterone.
  - Aldosterone increases sodium reabsorption in the tubules, leading to increased blood volume and pressure.
- Decreased sodium levels:
  - This also triggers the RAAS as it is sensed by juxtaglomerular apparatus.
- Increased sympathetic nervous system activity:
  - The release of norepinephrine and epinephrine from sympathetic nerves can activate the RAAS.

Effects of High Sodium Intake

High sodium intake increases extracellular fluid osmolarity which triggers thirst and expands plasma volume. This combination leads to increased venous return, higher end diastolic volume, and increased cardiac output, therefore increasing blood pressure.

Sodium, Hypertension, and Diuretics

Chronic high sodium intake can lead to physiological changes in the kidneys, making them less effective at eliminating sodium from the urine.
This can result in a persistent state of hypervolemia (increased blood volume).
Diuretics help inhibit the reabsorption of sodium, thus reducing blood volume and lowering blood pressure.

Summary of Blood Pressure Control

There are three phases of blood pressure control:
- Rapid control: This is mediated by the cardiovascular system and baroreceptors, leading to immediate responses to changes in blood pressure.
- Intermediate control: This occurs within minutes, involving RAAS activation and sodium retention, leading to increased blood volume and pressure.
- Long-term control: This occurs over hours, involving natriuresis and diuresis to regulate sodium and water levels to maintain optimal blood pressure.

Acid-Base Balance in the Kidney

Carbon dioxide (CO2) plays a crucial role in acid-base balance.
When oxygen enters cells, aerobic metabolism produces CO2, which leads to the formation of hydrogen (H+) and bicarbonate (HCO3-) ions.
Carbonic anhydrase is an enzyme that catalyzes the reactions involved in CO2 metabolism.
The kidneys eliminate H+ ions and reabsorb some HCO3- ions.
This reabsorbed bicarbonate enters the bloodstream and helps maintain a basic pH around 7.4.
The bicarbonate buffer system acts to maintain pH balance by reacting with H+ ions to form water (H2O) and CO2.
When pH becomes too acidic, the kidneys push out H+ ions more rapidly into the urine. Conversely, when pH becomes too basic, H+ ions are retained, and bicarbonate reabsorption is reduced.

Micturition Reflex (Urination)

The detrusor muscle, an involuntary muscle that contracts the bladder, receives sympathetic and parasympathetic innervation.
The internal sphincter, a circular muscle connecting the bladder to the urethra, is controlled by the autonomic nervous system (ANS).
The external urethral sphincter is under voluntary control.
Sympathetic innervation (L1-L2) relaxes the bladder and contracts the internal sphincter, inhibiting urination.
Parasympathetic innervation (S2-S4) contracts the bladder and relaxes the internal sphincter, facilitating urination
Pudendal nerve (S2-S4) controls the voluntary contraction of the external urethral sphincter, allowing for voluntary control over urination.

Spinal Cord Injury and Urinary Disfunction

Upper motor neuron bladder (spastic): This leads to a hyper-reflexive bladder, characterized by frequent contractions and incontinence.
Lower motor neuron bladder (flaccid): This results in a relaxed bladder that is unable to contract.
Both upper and lower motor neuron bladder conditions can lead to bladder incontinence, increased risk of urinary tract infections (UTIs), and bladder damage.
Urine back-up into the kidneys (hydronephrosis) can damage the kidneys.

Micturition

The bladder is a compliant tissue, meaning it can expand without a significant increase in pressure.
Micturition contractions occur when the bladder contracts and its volume decreases, triggering the urge to urinate.

Glomerular Filtration Rate (GFR)

GFR is the volume of plasma filtered by the kidneys per minute, typically 90-120 mL/min.
A sudden drop in GFR indicates acute kidney injury, while a gradual decrease over time suggests chronic kidney disease.
GFR generally declines slowly with age.
Auto-regulation allows the afferent and efferent arterioles to independently vasoconstrict and vasodilate, helping maintain GFR.
GFR can be measured using creatinine, a metabolic by-product of muscle metabolism.
Blood creatinine levels correlate with GFR. A poor GFR results in higher creatinine levels, indicating reduced kidney function.

Hypertension and the Kidney

Hypertension (high blood pressure) can have multiple negative effects on the kidneys:
- High blood pressure in the glomerulus can lead to glomerular hypertension, damaging the glomerulus over time through scarring and impaired function.
- Renal tubule damage can occur as a result of hypertension.
- Protein-losing nephropathy: This involves the leakage of protein into the urine caused by damaged glomeruli.
  - This decreases the plasma colloid osmotic pressure, hindering fluid reabsorption back into the bloodstream.
- Damage to arterioles can lead to thickening, fibrosis, and impaired function.
Chronic kidney disease can lead to multiple systemic effects, including:
- Impaired vitamin D synthesis
- Calcium homeostasis issues
- Reduced red blood cell production (anemia)
- Acid-base balance disturbances
- Sodium and potassium imbalances

Effects of Diabetes on the Kidney

High blood glucose levels in diabetes can negatively affect the glomerulus and renal tubule reabsorption:
- Glucose transporters become saturated, resulting in glucose being excreted in the urine (glycosuria).
- Reabsorption of glucose and sodium together can lead to elevated blood pressure and contribute to damage to the kidneys.
- Hyperfiltration occurs as the kidneys work harder to filter the excess glucose, leading to increased pressure in the glomerulus and potentially damaging it.

Exercise Prescription and the Kidney

Individuals with kidney dysfunction may experience:
- Increased fatigue, exercise intolerance, and delayed recovery from exercise.
- Impaired acid-base and electrolyte balance.
- Impaired muscular performance.
- Exacerbated muscle damage following exercise.
- Chronic kidney disease alters muscle metabolism over time.
- Development of peripheral neuropathies (nerve damage), increasing the risk of falls.
- Impaired vitamin D and calcium metabolism can alter bone health and increase fracture risk.
- Electrolyte imbalance and protein-losing nephropathy can lead to edema (swelling).
- Electrolyte imbalance and impaired muscle contraction can raise the risk of arrhythmias.
- Impaired oxygen sensing and erythropoietin secretion leads to low red blood cell count (anemia), further impairing exercise tolerance.
- Impaired renal function can affect drug metabolism, leading to prolonged drug action and potential toxicity.

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Description

Test your knowledge on kidney anatomy and its functions. This quiz covers the layers of the kidneys, the role of nephrons, and the renal vasculature. Perfect for students in anatomy or healthcare-related fields.

Human Physiology Week 7 - Notes