Part 5: Water and Ion Balance

How much water is there inside the body

How is the water distributed?

• Intracellular fluid

• Extracellular fluid

What contributes to the water in the body? - what does it average out to?

• Gains: 2 ways

  • Also state volume of water for each

• Loss: 5 ways

  • Also state volume of water for each

• about 55% of the body is composed of water

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Water distribution

• Intracellular: 2/3

• Extracellular fluid: 1/3

  • 75% of that interstitial fluid

  • 25% of that is in plasma

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Contributions

• Gain

  • through drinking or eating 2.2 L/day

  • Byproducts of metabolic products 0.3 L/day

• Loss

  • Urine 1.5 L/day

  • 0.9 L/day

    • Skin (sweat)

    • Lungs (breathing)

  • Feces: 0.1 L/day

• Gains and losses will be balanced to 0 L/day

Water Homeostasis

• What happens when there is too much water loss?

  • Diseases

  • What happens inside the body + symptoms

• What happens when there is too much water intake?

  • Where does the water go?

  • Symptoms

• Water loss

  • Diseases: hypotension/shock

  • Process: water loss → less extracellular fluid → lowered blood pressure

    • Symptoms: confused, chest pain, low blood pressure, no urine

• Too much water intake

  • Goes into the lungs, legs, abdomen

    • Difficulty breathing, walking, running etc

How is urine formed?

• which organ involved

• Explain process in the kidneys

  • Explain process of the main pathway of urine being formed

  • How much blood into the kidneys

  • How much waste is produced in the body

  • How much urine produced a day

• Based on the process, what does it tell us about the the kidneys filtering process?

• Kidney is involved

  • Blood —> kidney —> nephrons (where the blood plasma gets filtered) —> filter into ureter —> bladder —> urethra

• 1584 L into the kidneys

• 180 L filtrate formed a day

• 1.8 L of urine secreted/day

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Not all filtrate gets secreted

Nephron

• Explain the where the blood meets up with the nephron

• Why is the nephron so important?

  • 5 factors

• Explain the parts involved in blood filtration in the nephron

• Arterial blood → glomerulus (where it meets up with the nephron)

• Importance

  • Excreting waste

  • Regulates blood volume

  • Controls electrolytes

  • Blood pH

  • Vitamin D!!!!! (via PTH)

• Process

  • (filtrate from blood) → proximal tubule (osmolarity: 300) —> loop of henle (reabsorption) —> distal convolted tubule —> collecting duct portion

What three hormones regulate water, Na+, and K+ balance

• Just list them and how is water and/or Na+ and/or K+ affected by the hormone

Vasopressin

• up water reabsorption

Aldosterone

• up Na+ reabsorption

• K+ secretion

• has a very close relation with renin

Atrial natriuretic peptide

• Na+ and water reabsorption

• K+ reabsorption

Vasopressin

• Another name for it

• Primary function (based on name)

  • Purpose of function

• Secondary function

• Where is it synthesized

• Where is it secreted

• How is it regulated (the secretion)

  • 2 main factors

  • How it works (for both; but initally two slightly different pathway)

• How does the hormone work at the kidney

  • Explain the process and specifically where at the nephron (which part of it)

• A.k.a antiduiretic hormone or ADH

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• Primary anti = prevent urination = prevent water reabsorption

  • Purpose

    • Conserve body water

    • Water balance and fluid homeostasis

    • Increases blood volume and blood pressure

• Secondary function: regulating permeability of cells in the kidney

  • Purpose: to ensure reabsorption and low urine output

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• Synthesized in the hypothalamus

• Secreted from the posterior pituitary

  • But does not make the hormone

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Regulation

• Main factor: high plasma osmolarity (increase salt/ion)

  • Need to dilute = reserve water

  • Detected by the osmoreceptors in the hypothamus

• Second factor: low blood pressure

  • Detected by the reduced stretch of the walls of the atria of the heart and aortic and carotid arteries

• Both same pathway

  • Detected by the hypthamalic neurosecretory cells to secrete ADH into the posterior pituitary

  • The posterior pituitary will secreted the ADH

• Result: increased water permeability in the nephrons

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Process

• the vasopression goes to the kidney through the arteries and reaches thedistal convolted tubule and collecting duct, where the hormone binds to the receptors in these locations

• Results in signal cascade (for metabotropic pathway)

• aquaporin-2 water pores will be exocytosis to the apcical membrane (inside the tubule)

• the water pores allows the water to goes through the collecting duct cells, through the interstitial fluid and to the blood stream

Aldosterone

• what is it

• Where is it made in

• Main function

• In what area in the nephron does it affect

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• What is it’s stimulus (2 kinds)

• What type of feedback pathway does it follow

  • Types of it

• What stimulus inhibits it?

• A steroid

• Synthesized in the adrenal cortex (located right above the kidneys)

• Function: regulates sodium levels

  • Na+ reabsorption + retain water

  • K+ secretion

• Affects the distal tubule and the collecting duct

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Stimulus

• high potassium concentration

• Angiotensin 2 (blood pressure)

Pathway: negative feedback

• Simple (K+ concentrations)

• Complex (renin-angiotensin 2) (blood pressure)

Inhibitory

• high osmolarity in the extracellular fluid

Process for simple aldosterone pathways with high potassium concentration

• Process

  • Hormones in the blood stream reaches the kidneys

  • Goes through the blood, through the interstitial fluid, and into the distal collecting duct cells to bind with the cytoplasmic receptor

  • The complex initiates transcription in the nucleus (translocates there) to make new protein channels on the apical membrane (side facing towards the lumen of the nephron) and pumps on the basal membrane (facing towards blood)

    • Channels in charge of the secretion and reabsorption

    • ATPase pumps are in charge of the transportation of ions in between the

  • The new proteins will also modulate the existing ones

    • ***by prevent degradation of the apical Na+ channel and the increase expression of the Na+ and K+ channels on the apical membrane and the ATPase pump Na+/K+ on the basal membrane

Process for complex aldosterone negative feedback pathway

• state stimulus

• than process

• then three affects

• The renal juxtaglomerular cells located on the arterioles near the glomerulus secrete enzyme renin with blood pressure falls

• Kidney secreted renin

• Liver produces precursor angiotensinogen which renin cleaves to angiotensin I

• Lungs have ACE which cuts the precursor to angiotensin II

• Affects

  • Hypothalamus: Thirst and drinking

  • Blood vessels: Vasoconstriction

  • Adrenal cortex produce aldosterone secretion → kidney undergoes salt and water retention

• Results: increase in blood pressure

Natriuretic peptides

• main function

• What produces them

• 3 types

  • Their own functions

  • Where is it secreted from

• main function: decrease water retention

• Produced by secondary endocrine glands (have secondary function)

• e.g

  • ANP: sense the stretch of the heart = high pressure = must dilate them and secrete fluids

    • Secreted by Atria (myocardia cells) and neurons

  • BNP

    • secreted by the ventricles myocardial cells and neurons

  • CNP

    • Secreted by the brain, pituitary glands, vessels, and kidneys

• Main process

  • hypothalamus secreted less vasopressin

  • Kidney secretes less renin and increase globular filtrate rate

  • Adrenal cortex secreted less aldosterone

  • Medulla oblongata have decreased sympathetic output