The Kidneys

The kidneys are the primary functional organ of the renal system.

They are essential in homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and the regulation of blood pressure (by maintaining salt and water balance).

They serve the body as a natural filter of the blood and remove wastes that are excreted through the urine.

They are also responsible for the reabsorption of water, glucose, and amino acids, and will maintain the balance of these molecules in the body.

In addition, the kidneys produce hormones including calcitriol, erythropoietin, and the enzyme renin, which are involved in renal and hemotological physiological processes.

Anatomical Location

The kidneys are a pair of bean-shaped, brown organs about the size of your fist. They are covered by the renal capsule, which is a tough capsule of fibrous connective tissue.

Right kidney being slightly lower than the left, and left kidney being located slightly more medial than the right.

The right kidneys lie  just below the diaphragm and posterior to the liver, the left below the diaphragm and posterior to the spleen.

Resting on top of each kidney is an adrenal gland (adrenal meaning on top of renal), which are involved in some renal system processes despite being a primarily endocrine organ.

They are considered retroperitoneal, which means that they lie behind the peritoneum, the membrane lining of the abdominal cavity.

The renal artery branches off from the lower part of the aorta and provides the blood supply to the kidneys.

 Renal veins take blood away from the kidneys into the inferior vena cava.

The ureters are structures that come out of the kidneys, bringing urine downward into the bladder.

Internal Anatomy of the Kidneys

There are three major regions of the kidney:

1.         Renal cortex

2.         Renal medulla

3.         Renal pelvis

The renal cortex is a space between the medulla and the outer capsule.

The renal medulla contains the majority of the length of nephrons, the main functional component of the kidney that filters fluid from blood.

The renal pelvis connects the kidney with the circulatory and nervous systems from the rest of the body.

Renal Cortex

The kidneys are surrounded by a renal cortex

The cortex provides a space for arterioles and venules from the renal artery and vein, as well as the glomerular capillaries, to perfuse the nephrons of the kidney. Erythropotein, a hormone necessary for the synthesis of new red blood cells, is also produced in the renal cortex.

Renal Medulla

The medulla is the inner region of the parenchyma of the kidney. The medulla consists of multiple pyramidal tissue masses, called the renal pyramids, which are triangle structures that contain a dense network of nephrons.

At one end of each nephron, in the cortex of the kidney, is a cup-shaped structure called the Bowman's capsule. It surrounds a tuft of capillaries called the glomerulus that carries blood from the renal arteries into the nephron, where plasma is filtered through the capsule.

After entering the capsule, the filtered fluid flows along the proximal convoluted tubule to the loop of Henle and then to the distal convoluted tubule and the collecting ducts, which flow into the ureter. Each of the different components of the nephrons are selectively permeable to different molecules, and enable the complex regulation of water and ion concentrations in the body.

Renal Pelvis

The renal pelvis contains the hilium. The hilum is the concave part of the bean-shape where blood vessels and nerves enter and exit the kidney; it is also the point of exit for the ureters—the urine-bearing tubes that exit the kidney and empty into the urinary bladder. The renal pelvis connects the kidney to the rest of the body.

Supply of Blood and Nerves to the Kidneys

•  The renal arteries branch off of the abdominal aorta and supply the kidneys with blood. The arterial supply of the kidneys varies from person to person, and there may be one or more renal arteries to supply each kidney.

•  The renal veins are the veins that drain the kidneys and connect them to the inferior vena cava.

•  The kidney and the nervous system communicate via the renal plexus. The sympathetic nervous system will trigger vasoconstriction and reduce renal blood flow, while parasympathetic nervous stimulation will trigger vasodilation and increased blood flow.

•  Afferent arterioles branch into the glomerular capillaries, while efferent arterioles take blood away from the glomerular capillaries and into the interlobular capillaries that provide oxygen to the kidney.

•  renal vein

The veins that drain the kidney and connect the kidney to the inferior vena cava.

•  renal artery

These arise off the side of the abdominal aorta, immediately below the superior mesenteric artery, and supply the kidneys with blood.

Red Blood Cells (erythrocytes)

• Women average about 4.8 million of these cells per cubic millimeter (mm³; which is the same as a microliter [µl]) of blood.
• Men average about 5.4 x 10⁶ per µl.
• These values can vary over quite a range depending on such factors as health and altitude.
• RBC precursors mature in the bone marrow closely attached to a macrophage.
• They manufacture hemoglobin until it accounts for some 90% of the dry weight of the cell.

• The nucleus is squeezed out of the cell and is ingested by the macrophage.

RBC have characteristic biconcave shape

Thus RBCs are terminally differentiated; that is, they can never divide. They live about 120 days and then are ingested by phagocytic cells in the liver and spleen. Most of the iron in their hemoglobin is reclaimed for reuse. The remainder of the heme portion of the molecule is degraded into bile pigments and excreted by the liver. Some 3 million RBCs die and are scavenged by the liver each second.

Red blood cells are responsible for the transport of oxygen and carbon dioxide.

The Body Regulates pH in Several Ways

• Buffers are weak acid mixtures (such as bicarbonate/CO₂) which minimize pH change
  • Buffer is always a mixture of 2 compounds
    • One compound takes up H ions if there are too many (H acceptor)
    • The second compound releases H ions if there are not enough (H donor)
  • The strength of a buffer is given by the buffer capacity
    • Buffer capacity is proportional to the buffer concentration and to a parameter known as the pK
  • Mouth bacteria produce acids which attack teeth, producing caries (cavities). People with low buffer capacities in their saliva have more caries than those with high buffer capacities.
• CO₂ gas (a potential acid) is eliminated by the lungs
• Other acids and bases are eliminated by the kidneys

Proteins:

• about 50 - 60% of the dry mass of a typical cell
• subunit is the amino acid & amino acids are linked by peptide bonds
• 2 functional categories = structural (proteins part of the structure of a cell like those in the cell membrane) & enzymes

Enzymes are catalysts. Enzymes bind temporarily to one or more of the reactants of the reaction they catalyze. In doing so, they lower the amount of activation energy needed and thus speed up the reaction

PHYSIOLOGY OF THE BRAIN

• The Cerebrum (Telencephalon) Lobes of the cerebral cortex

   

  1. Frontal Lobe
     1. Precentral gyrus, Primary Motor Cortex, point to point motor neurons, pyramidal cells: control motor neurons of the brain and spinal cord. See Motor homunculus
     2. Secondary Motor Cortex repetitive patterns
     3. Broca's Motor Speech area
     4. Anterior - abstract thought, planning, decision making, Personality
  2. Parietal Lobe
     1. Post central gyrus, Sensory cortex, See Sensory homunculus, size proportional to sensory receptor density.
     2. Sensory Association area, memory of sensations
  3. Occipital Lobe
     1. Visual cortex, sight (conscious perception of vision)
     2. Visual Association area, correlates visual images with previous images, (memory of vision, )
  4. Temporal Lobe
     1. Auditory Cortex, sound
     2. Auditory Association area, memory of sounds
  5. Common Integratory Center - angular gyrus, Parietal, Temporal & Occipital lobes
     1. One side becomes dominent, integrats sensory (somesthetic, auditory, visual) information
  6. The Basal nuclei (ganglia)
     1. Grey matter (cell bodies) within the White matter of cerebrum, control voluntary movements
  7. Cauadate nucles - chorea (rapi, uncontrolled movements), Parkinsons: (dopamine neurons of substantia nigra to caudate nucles) jerky movements, spasticity, tremor, blank facial expression
  8. The limbic system - ring around the brain stem, emotions(w/hypothalamus), processing of olfactory information

• The Diencephalon

   

  1. The Thalamus - Sensory relay center to cortex (primitive brain!)
  2. The Hypothalamus
     1. core temperature control"thermostat", shivering and nonshivering thermogenesis
     2. hunger & satiety centers, wakefulness, sleep, sexual arousal,
     3. emotions (w/limbic-anger, fear, pain, pleasure), osmoregulation, (ADH secretion),
     4. Secretion of ADH, Oxytocin, Releasing Hormones for Anterior pitutary
     5. Linkage of nervous and endocrine systems

• The Mesencephalon or Midbrain -

   

  1. red nucleus, motor coordination (cerebellum/Motor cortex),
  2. substantia nigra
• The Metencephalon
  1. The Cerebellum -
     1. Performs automatic adjustments in complex motor activities
     2. Input from Proprioceptors (joint, tendon, muscles), position of body in Space
        1. Motor cortex, intended movements (changes in position of body in Space)
     3. Damping (breaking motor function), Balance, predicting, inhibitory function of Purkinji cells (GABA), speed, force, direction of movement
  2. The Pons - Respiratory control centers (apneustic, pneumotaxic)
     1. Nuclei of cranial nerves V, VI, VII, VIII

• Myelencephalon

   

  1. The Medulla
     1. Visceral motor centers (vasomotor, cardioinhibtory, respiratory)
     2. Reticular Formation RAS system, alert cortex to incoming signals, maintenance of consciousness, arousal from sleep
     3. All Afferent & Efferent fibers pass through, crossing over of motor tracts
  2. Corpus Callosum: Permits communication between cerebralhemispheres
• Generalized Brain Avtivity
  1. Brain Activity and the Electroencephalogram(EEG)
     1. alpha waves: resting adults whose eyes are closed
     2. beta waves: adults concentrating on a specific task;
     3. theta waves: adults under stress;
     4. delta waves: during deep sleep and in clinical disorders
  2. Brain Seizures
     1. Grand Mal: generalized seizures, involvs gross motor activity, affects the individual for a matter or hours
     2. Petit mal: brief incidents, affect consciousness but may have no obvious motor abnormalities
  3. Chemical Effects on the Brain
     1. Sedatives: reduce CNS activity
     2. Analgesics: relieve pain by affecting pain pathways or peripheral sensations
     3. Psychotropics: alter mood and emotional states
     4. Anticonvulsants: control seizures
     5. Stimulants: facilitate CNS activity
  4. Memory and learning
     1. Short-term, or primary, memories last a short time, immediately accessible (phone number)
     2. Secondary memories fade with time (your address at age 5)
     3. Tertiary memories last a lifetime (your name)
     4. Memories are stored within specific regions of the cerebral cortex.
     5. Learning, a more complex process involving the integration of memories and their use to direct or modify behaviors
     6. Neural basis for memory and learning has yet to be determined.
• Fibers in CNS
  1. Association fibers: link portions of the cerebrum;
  2. Commissural fibers: link the two hemispheres;
  3. Projection fibers: link the cerebrum to the brain stem

Oxygen Transport

In adult humans the hemoglobin (Hb) molecule

• consists of four polypeptides:
  • two alpha (α) chains of 141 amino acids and
  • two beta (β) chains of 146 amino acids
• Each of these is attached the prosthetic group heme.
• There is one atom of iron at the center of each heme.
• One molecule of oxygen can bind to each heme.

The reaction is reversible.

• Under the conditions of lower temperature, higher pH, and increased oxygen pressure in the capillaries of the lungs, the reaction proceeds to the right. The purple-red deoxygenated hemoglobin of the venous blood becomes the bright-red oxyhemoglobin of the arterial blood.
• Under the conditions of higher temperature, lower pH, and lower oxygen pressure in the tissues, the reverse reaction is promoted and oxyhemoglobin gives up its oxygen.