NEET MDS Lessons
Physiology
The pancreas
The pancreas consists of clusters if endocrine cells (the islets of Langerhans) and exocrine cells whose secretions drain into the duodenum.
Pancreatic fluid contains:
- sodium bicarbonate (NaHCO3). This neutralizes the acidity of the fluid arriving from the stomach raising its pH to about 8.
- pancreatic amylase. This enzyme hydrolyzes starch into a mixture of maltose and glucose.
- pancreatic lipase. The enzyme hydrolyzes ingested fats into a mixture of fatty acids and monoglycerides. Its action is enhanced by the detergent effect of bile.
- 4 zymogens— proteins that are precursors to active proteases. These are immediately converted into the active proteolytic enzymes:
- trypsin. Trypsin cleaves peptide bonds on the C-terminal side of arginines and lysines.
- chymotrypsin. Chymotrypsin cuts on the C-terminal side of tyrosine, phenylalanine, and tryptophan residues (the same bonds as pepsin, whose action ceases when the NaHCO3 raises the pH of the intestinal contents).
- elastase. Elastase cuts peptide bonds next to small, uncharged side chains such as those of alanine and serine.
- carboxypeptidase. This enzyme removes, one by one, the amino acids at the C-terminal of peptides.
- nucleases. These hydrolyze ingested nucleic acids (RNA and DNA) into their component nucleotides.
The secretion of pancreatic fluid is controlled by two hormones:
- secretin, which mainly affects the release of sodium bicarbonate, and
- cholecystokinin (CCK), which stimulates the release of the digestive enzymes.
Each hormone in the body is unique. Each one is different in it's chemical composition, structure, and action. With respect to their chemical structure, hormones may be classified into three groups: amines, proteins, and steroids.
Amines- these simple hormones are structural variation of the amino acid tyrosine. This group includes thyroxine from the thyroid gland and epinephrine and norepinephrine from the adrenal medulla.
Proteins- these hormones are chains of amino acids. Insulin from the pancreas, growth hormone from the anterior pituitary gland, and calcitonin from the thyroid gland are all proteins. Short chains of amino acids are called peptides. Antidiuretic hormone and oxytocin, synthesized by the hypothalamus, are peptide hormones.
Steroids- cholesterol is the precursor for the steroid hormones, which include cortisol and aldosterone from the adrenal cortex, estrogen and progesterone from the ovaries, and testosterone from the testes.
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There Are 12 Pairs of Cranial Nerves
- The 12 pairs of cranial nerves emerge mainly from the ventral surface of the brain
- Most attach to the medulla, pons or midbrain
- They leave the brain through various fissures and foramina of the skull
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Nerve
Name
Sensory
Motor
Autonomic
ParasympatheticI
Olfactory
Smell
II
Optic
Vision
III
Oculomotor
Proprioception
4 Extrinsic eye muscles
Pupil constriction
Accomodation
FocusingIV
Trochlear
Proprioception
1 Extrinsic eye muscle (Sup.oblique)
V
Trigeminal
Somatic senses
(Face, tongue)Chewing
VI
Abducens
Proprioception
1 Extrinsic eye muscle (Lat. rectus)
VII
Facial
Taste
Proprioception
Muscles of facial expression
Salivary glands
Tear glandsVIII
Auditory
(Vestibulocochlear)Hearing, Balance
IX
Glossopharyngeal
Taste
Blood gasesSwallowing
GaggingSalivary glands
X
Vagus
Blood pressure
Blood gases
TasteSpeech
Swallowing GaggingMany visceral organs
(heart, gut, lungs)XI
Spinal acessory
Proprioception
Neck muscles:
Sternocleidomastoid
TrapeziusXII
Hypoglossal
Proprioception
Tongue muscles
Speech - Many of the functions that make us distinctly human are controlled by cranial nerves: special senses, facial expression, speech.
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Cranial Nerves Contain Sensory, Motor and Parasympathetic Fibers
Acute Obstructive Disorders
1. Heimlich maneuver
2. Bypass, tracheostomy w/catheter to suck up secretion
The hypothalamus is a region of the brain. It secretes a number of hormones.
- Thyrotropin-releasing hormone (TRH)
- Gonadotropin-releasing hormone (GnRH)
- Growth hormone-releasing hormone (GHRH)
- Corticotropin-releasing hormone (CRH)
- Somatostatin
- Dopamine
All of these are released into the blood, travel immediately to the anterior lobe of the pituitary, where they exert their effects.
Two other hypothalamic hormones:
- Antidiuretic hormone (ADH) and
- Oxytocin
travel in neurons to the posterior lobe of the pituitary where they are released into the circulation.
Functional Divisions of the Nervous System:
1) The Voluntary Nervous System - (ie. somatic division) control of willful control of effectors (skeletal muscles) and conscious perception. Mediates voluntary reflexes.
2) The Autonomic Nervous System - control of autonomic effectors - smooth muscles, cardiac muscle, glands. Responsible for "visceral" reflexes
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.