Introduction to optometry foundation year at city university of london Introductory biological sciences module Lesson 18 about the kidney. Everything you need to know about the Kidney in the course.
Kidney
Location and external anatomy
- 6cm in diameter, 11cms high, 3cms thick
- Large, bean-shaped organs
- Lateral side- convex shape
- Medial (towards the middle)- concave shape
- With a vertical cleft, renal hilum
Ureter and renal blood supply join kidney at the hilum,
renal sinus, adrenal glands sits on top
Kidney functions- Homeostasis
1. Osmoregulation, control of total body water volume
2. Electrolyte balance, body fluid ‘osmolality’, concentration
of solutes in blood
3. Acid-base (pH) balance
4. Toxic wastes, filters blood plasma (~200 L/day) supplied by
renal artery, no alternative means of excerpting metabolic
wastes; urea, uric acid or creatinine, drugs, other toxins
5. Produces Erythropoietin & renin, blood cell production & blood
pressure
6. Converts VitD to active form
7. Starvation, metabolism and gluconeogenesis
Normal urine- Differs from filtered blood plasma:
1- 91-96% water & rest dissolved solutes (higher concentration than
plasma), including:
Salt (Na+, Cl-), other electrolytes (K+, H+, HCO3-)
2- No cells, nutrients or plasma proteins
3- slightly acidic (pH 5.5-6.0), urea & Uric acid (nitrogenous waste from
amino acid & nucleic acid metabolism), creatinine (muscle waste from
ATP metabolism)
0.6L-2.6L urine produced per day by healthy adult
6-8 urinations per day (~350ml bladder capacity)
3 key regions
1. Cortex - light appearance
2. Medulla- dark reddish-brown, stripped, bundles of capillaries
and collecting tubes, pyramids separated by renal columns
3. Pelvis- funnel shaped tube, continuous with ureter, fed by
calyces
The nephron
Functional unit=
the nephron ~3cm long
1-renal artery crosses pelvis/ calyces
2-Interlobar arteries ascend renal
columns
, 3-afferent arterioles supply glomerular capillaries for plasma filtration at bowman’s capsule
4- efferent arterioles drain glomeruli
5- peritubular capillaries around PCT & DCT reclaim
reabsorbed substances
6- & vasa recta (straight vessels) in medulla parallel
to Loop of Henle, for water/ion exchange
Nephrons & vascular relations: peritubular & vasa
recta capillaries
Consider 3 main functions
1- filtration: between the
glomerulus/bowman’s capsule/ renal
corpuscle
2- reabsorption: by the proximal
convoluted tubule & Loop of Henle
3- secretion: by the distal convoluted
tubule
Plasma filtration
1- Blood enters glomerulus under pressure
- due to afferent arteriole
2- Glomerular endothelial wall is fenestrated
- plasma (not cells) forced through the pores
3- Bowman’s capsule podocytes wrap around the
glomerular capillaries
4- Plasma passes through filtration slits between
adjoining podocytes
- to enter lumen bowman’s capsule & then the
PCT
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