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Mammalian kidney

Mammalian kidney is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Mammalian kidney rather than just read about it. In short: The mammalian kidneys are a pair of excretory organs of the urinary system of mammals, being functioning kidneys in postnatal-to-adult individuals (i.e. metanephric kidneys). The kidneys in mammals are usually bean-shaped or externally lobulated.

Mammalian kidney — main illustration
Mammalian kidney — illustration

Key takeaways

  • Mammalian kidney belongs to biology; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Mammalian kidney to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Mammalian kidney from memory before moving on to harder problems.

Reference excerpt

The mammalian kidneys are a pair of excretory organs of the urinary system of mammals, being functioning kidneys in postnatal-to-adult individuals (i.e. metanephric kidneys). The kidneys in mammals are usually bean-shaped or externally lobulated. They are located behind the peritoneum (retroperitoneally) on the back (dorsal) wall of the body. The typical mammalian kidney consists of a renal capsule, a peripheral cortex, an internal medulla, one or more renal calyces, and a renal pelvis. Although the calyces or renal pelvis may be absent in some species. The medulla is made up of one or more renal pyramids, forming papillae with their innermost parts. Generally, urine produced by the cortex and medulla drains from the papillae into the calyces, and then into the renal pelvis, from which urine exits the kidney through the ureter. Nitrogen-containing waste products are excreted by the kidneys in mammals mainly in the form of urea. The structure of the kidney differs between species. The kidneys can be unilobar (a single lobe represented by a single renal pyramid) or multilobar, unipapillary (a single or a common papilla), with several papillae or multipapillary, may be smooth-surfaced or lobulated. The multilobar kidneys can also be reniculate, which are found mainly in marine mammals. The unipapillary kidney with a single renal pyramid is the simplest type of kidney in mammals, from which the more structurally complex kidneys are believed to have evolved. Differences in kidney structure are the result of adaptations during evolution to variations in body mass and habitats (in particular, aridity) between species. The cortex and medulla of the kidney contain nephrons, each of which consists of a glomerulus and a complex tubular system. The cortex contains glomeruli and is responsible for filtering the blood. The medulla is responsible for urine concentration and contains tubules with short and long loops of Henle. The loops of Henle are essential for urine concentration. Amongst the vertebrates, only mammals and birds have kidneys that can produce urine more concentrated (hypertonic) than the blood plasma, but only in mammals do all nephrons have the loop of Henle. The kidneys of mammals are vital organs that maintain water, electrolyte and acid-base balance in the body, excrete nitrogenous waste products, regulate blood pressure, and participate in bone formation and regulation of glucose levels. The processes of blood plasma filtration, tubular reabsorption and tubular secretion occur in the kidneys, and urine formation is a result of these processes. The kidneys produce renin and erythropoietin hormones, and are involved in the conversion of vitamin D to its active form. Mammals are the only class of vertebrates in which only the kidneys are responsible for maintaining the homeostasis of the extracellular fluid in the body. The function of the kidneys is regulated by the autonomic nervous system and hormones. The potential for regeneration in mature kidneys is limited because new nephrons cannot be formed. In cases of limited injury, renal function can be restored through compensatory mechanisms. The kidneys can have noninfectious and infectious diseases; in rare cases, congenital and hereditary anomalies occur in the kidneys of mammals. Pyelonephritis is usually caused by bacterial infections. Some diseases may be species-specific, and parasitic kidney diseases are common in some species. The structural characteristics of the mammalian kidneys make them vulnerable to ischemic and toxic injuries. Permanent damage can lead to chronic kidney disease. Ageing of the kidneys also causes changes in them, and the number of functioning nephrons decreases with age.

Structure

Gross anatomy

Location and shape In mammals, the kidneys are usually bean-shaped; the shape is unique to mammals (fish, for example, have elongated kidneys). Some species have externally lobulated kidneys, as in marine mammals, bovines and bears. The lobulated kidneys of cetacians and pinnipeds have elongated oval shape. The concave part of the bean-shaped kidneys is called the renal hilum, through which the renal artery and nerves enter the kidney. The renal vein, collecting lymphatic vessels and ureter exit the kidney through the renal hilum. The kidneys are located retroperitoneally on the back (dorsal) wall of the body of mammals. In the body, the kidney is surrounded or partially surrounded by a layer of fatty tissue (perirenal adipose capsule), which separates the kidney from the perirenal fascia.

General structure The outer layer of each kidney is made up of a fibrous sheath called a renal capsule. The peripheral layer of the kidney is called the cortex, and the inner layer is called the medulla. The medulla consists of pyramids (also called malpighian pyramids), ascending with their base to the cortex and forming together with it the renal lobe. The pyramids are separated from each other by renal columns (Bertin's columns) formed by cortical tissue. The tips of the pyramids end with the renal papillae, from which urine is excreted into the calyces, pelvis, ureter, and, in most species, directly into the bladder, after which it is excreted through the urethra.

Parenchyma

… excerpt ends here. Continue reading the full article.

Illustrations

Mammalian kidney illustration
Mammalian kidney: Didactic model of the multilobar mammalian kidney:[51] .mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline ul,.mw-parser-output .hlist dl dl,.mw-parser-output .hlist dl ol,.mw-parser-output .hlist dl ul,.mw-parser-output .hlist ol dl,.mw-parser-output .hlist ol ol,.mw-parser-output .hlist ol ul,.mw-parser-output .hlist ul dl,.mw-parser-output .hlist ul ol,.mw-parser-output .hlist ul ul{display:inline}.mw-parser-output .hlist .mw-empty-li{display:none}.mw-parser-output .hlist dt::after{content:": "}.mw-parser-output .hlist dd::after,.mw-parser-output .hlist li::after{content:"\a0 · ";font-weight:bold}.mw-parser-output .hlist dd:last-child::after,.mw-parser-output .hlist dt:last-child::after,.mw-parser-output .hlist li:last-child::after{content:none}.mw-parser-output .hlist dd dd:first-child::before,.mw-parser-output .hlist dd dt:first-child::before,.mw-parser-output .hlist dd li:first-child::before,.mw-parser-output .hlist dt dd:first-child::before,.mw-parser-output .hlist dt dt:first-child::before,.mw-parser-output .hlist dt li:first-child::before,.mw-parser-output .hlist li dd:first-child::before,.mw-parser-output .hlist li dt:first-child::before,.mw-parser-output .hlist li li:first-child::before{content:" (";font-weight:normal}.mw-parser-output .hlist dd dd:last-child::after,.mw-parser-output .hlist dd dt:last-child::after,.mw-parser-output .hlist dd li:last-child::after,.mw-parser-output .hlist dt dd:last-child::after,.mw-parser-output .hlist dt dt:last-child::after,.mw-parser-output .hlist dt li:last-child::after,.mw-parser-output .hlist li dd:last-child::after,.mw-parser-output .hlist li dt:last-child::after,.mw-parser-output .hlist li li:last-child::after{content:")";font-weight:normal}.mw-parser-output .hlist ol{counter-reset:listitem}.mw-parser-output .hlist ol>li{counter-increment:listitem}.mw-parser-output .hlist ol>li::before{content:" "counter(listitem)"\a0 "}.mw-parser-output .hlist dd ol>li:first-child::before,.mw-parser-output .hlist dt ol>li:first-child::before,.mw-parser-output .hlist li ol>li:first-child::before{content:" ("counter(listitem)"\a0 "}1. Fibrous capsule2. Cortex3. Renal pyramid of the medulla4. Renal column of the cortex5. Nephron6. Renal papilla7. Minor renal calyx8. Major renal calyx9. Renal pelvis10. Ureter11. Renal artery12. Renal vein13. Interlobar artery14. Renal lobe15. Arcuate artery16. Interlobular artery.
Didactic model of the multilobar mammalian kidney:[51] .mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline ul,.mw-parser-output .hlist dl dl,.mw-parser-output .hlist dl ol,.mw-parser-output .hlist dl ul,.mw-parser-output .hlist ol dl,.mw-parser-output .hlist ol ol,.mw-parser-output .hlist ol ul,.mw-parser-output .hlist ul dl,.mw-parser-output .hlist ul ol,.mw-parser-output .hlist ul ul{display:inline}.mw-parser-output .hlist .mw-empty-li{display:none}.mw-parser-output .hlist dt::after{content:": "}.mw-parser-output .hlist dd::after,.mw-parser-output .hlist li::after{content:"\a0 · ";font-weight:bold}.mw-parser-output .hlist dd:last-child::after,.mw-parser-output .hlist dt:last-child::after,.mw-parser-output .hlist li:last-child::after{content:none}.mw-parser-output .hlist dd dd:first-child::before,.mw-parser-output .hlist dd dt:first-child::before,.mw-parser-output .hlist dd li:first-child::before,.mw-parser-output .hlist dt dd:first-child::before,.mw-parser-output .hlist dt dt:first-child::before,.mw-parser-output .hlist dt li:first-child::before,.mw-parser-output .hlist li dd:first-child::before,.mw-parser-output .hlist li dt:first-child::before,.mw-parser-output .hlist li li:first-child::before{content:" (";font-weight:normal}.mw-parser-output .hlist dd dd:last-child::after,.mw-parser-output .hlist dd dt:last-child::after,.mw-parser-output .hlist dd li:last-child::after,.mw-parser-output .hlist dt dd:last-child::after,.mw-parser-output .hlist dt dt:last-child::after,.mw-parser-output .hlist dt li:last-child::after,.mw-parser-output .hlist li dd:last-child::after,.mw-parser-output .hlist li dt:last-child::after,.mw-parser-output .hlist li li:last-child::after{content:")";font-weight:normal}.mw-parser-output .hlist ol{counter-reset:listitem}.mw-parser-output .hlist ol>li{counter-increment:listitem}.mw-parser-output .hlist ol>li::before{content:" "counter(listitem)"\a0 "}.mw-parser-output .hlist dd ol>li:first-child::before,.mw-parser-output .hlist dt ol>li:first-child::before,.mw-parser-output .hlist li ol>li:first-child::before{content:" ("counter(listitem)"\a0 "}1. Fibrous capsule2. Cortex3. Renal pyramid of the medulla4. Renal column of the cortex5. Nephron6. Renal papilla7. Minor renal calyx8. Major renal calyx9. Renal pelvis10. Ureter11. Renal artery12. Renal vein13. Interlobar artery14. Renal lobe15. Arcuate artery16. Interlobular artery.
Mammalian kidney: Simplified structure of the mammalian kidney lobe:[21][62] 1. Cortex2. Outer medulla3. Inner medulla4. Inner stripe5. Outer stripe6. Juxtamedullary nephron with long loop of Henle7. Medullary ray8. Renal capsule9. Renal papilla. .mw-parser-output .legend{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .legend-color{display:inline-block;min-width:1.25em;height:1.25em;line-height:1.25;margin:1px 0;text-align:center;border:1px solid black;background-color:transparent;color:black}.mw-parser-output .legend-text{}  Podocytes   Proximal convoluted tubule   Proximal straight tubule   Intermediate tubule (loop of Henle)   Distal straight tubule   Macula densa   Distal convoluted tubule   Connecting tubule   Collecting duct
Simplified structure of the mammalian kidney lobe:[21][62] 1. Cortex2. Outer medulla3. Inner medulla4. Inner stripe5. Outer stripe6. Juxtamedullary nephron with long loop of Henle7. Medullary ray8. Renal capsule9. Renal papilla. .mw-parser-output .legend{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .legend-color{display:inline-block;min-width:1.25em;height:1.25em;line-height:1.25;margin:1px 0;text-align:center;border:1px solid black;background-color:transparent;color:black}.mw-parser-output .legend-text{}  Podocytes   Proximal convoluted tubule   Proximal straight tubule   Intermediate tubule (loop of Henle)   Distal straight tubule   Macula densa   Distal convoluted tubule   Connecting tubule   Collecting duct
Mammalian kidney: Variation of the kidney between domestic mammalian species:[84](A) Equine kidneys with heart-shaped right kidney(B) Bovine kidneys with lobulated cortex and fused medulla(C) Canine bean-shaped kidneys.
Variation of the kidney between domestic mammalian species:[84](A) Equine kidneys with heart-shaped right kidney(B) Bovine kidneys with lobulated cortex and fused medulla(C) Canine bean-shaped kidneys.
Mammalian kidney: Author's drawing of a dolphin reniculate kidney:[91] 1. Renal artery2. Renal vein3. Common collecting duct that becomes the ureter.
Author's drawing of a dolphin reniculate kidney:[91] 1. Renal artery2. Renal vein3. Common collecting duct that becomes the ureter.

Worked examples

Example 1 — a first encounter with Mammalian kidney

Start with the simplest possible case. Write down what Mammalian kidney claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Mammalian kidney before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Mammalian kidney ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Mammalian kidney

In research
Mammalian kidney appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Mammalian kidney in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Mammalian kidney is common in secondary-school and first-year university syllabi. It links to neighbouring topics Kidney, Mammal anatomy, so understanding it makes those chapters shorter.
In everyday life
Look for Mammalian kidney outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Mammalian kidney in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Mammalian kidney means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Mammalian kidney out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mammalian kidney in simple terms?

The mammalian kidneys are a pair of excretory organs of the urinary system of mammals, being functioning kidneys in postnatal-to-adult individuals (i.e. metanephric kidneys). The kidneys in mammals are usually bean-shaped or externally lobulated.

Why does Mammalian kidney matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Mammalian kidney?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Mammalian kidney.

Tags

  • Kidney
  • Mammal anatomy

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