Regulating Blood Water Content (WJEC GCSE Biology)

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Regulating Blood Water Content

  • The regulation of blood water content involves maintaining water and salt concentrations within the blood; this is an example of homeostasis
    • This is vital to prevent harmful changes occurring to cells of the body as a result of osmosis
  • The kidneys regulate the water content of the blood by removing water from the body in the urine
  • The volume of urine varies depending on the blood water content
    • When blood water content is high a large volume of dilute urine is produced
    • When blood water content is low a small volume of concentrated urine is produced
  • The colour of urine can be an indicator of concentration:
    • Dilute urine is usually pale in colour because it contains a lot of water in relation to solutes
    • Concentrated urine is darker in colour because it contains little water in relation to solutes

Role of ADH

Higher Tier Only

  • The control of water reabsorption by the tubules is an example of negative feedback
  • Water reabsorption is controlled by the hormone ADH, which affects the permeability of the tubules to water

Low blood water content

  • If the water content of the blood is too low:
    • The brain detects the decreased water content of the blood
    • The pituitary gland in the brain releases more ADH 
    • ADH causes the kidneys tubules to reabsorb more water
    • The kidneys produce a small volume of concentrated urine

ADH and low blood water content diagram ADH and low blood water content 

When blood water content is low the brain releases more ADH; this causes increased water reabsorption by the kidneys

High blood water content

  • If the water content of the blood is too high:
    • The brain detects high blood water content
    • The pituitary gland releases less ADH
    • ADH causes the kidneys to reabsorb less water
    • The kidneys produce a large volume of dilute urine

ADH and high blood water content diagram

ADH and high blood water content

When blood water content is high the brain releases less ADH; this causes decreased water reabsorption by the kidneys

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Emma

Author: Emma

Expertise: Biology

Prior to working at SME, Emma was a Biology teacher for 5 years. During those years she taught three different GCSE exam boards and two A-Level exam boards, gaining a wide range of teaching expertise in the subject. Emma particularly enjoys learning about ecology and conservation. Emma is passionate about making her students achieve the highest possible grades in their exams by creating amazing revision resources!