Hypoxia

• Hypoxia is tissue oxygen deficiency
• Brain is the most sensitive tissue to hypoxia: complete lack of oxygen can cause unconsciousness in 15 sec and irreversible damage within 2 min.
• Oxygen delivery and use can be interrupted at several sites

• Causes:
  • Hypoxic: high altitude, pulmonary edema, hypoventilation, emphysema, collapsed lung
  • Anemic: iron deficiency, hemoglobin mutations, carbon monoxide poisoning
  • Ischemic: shock, heart failure, embolism
  • Histotoxic: cyanide poisoning (inhibits mitochondria)

• Carbon monoxide (CO) poisoning:
  • CO binds to the same heme Fe atoms that O₂ binds to
  • CO displaces oxygen from hemoglobin because it has a 200X greater affinity for hemoglobin.
  • Treatment for CO poisoning: move victim to fresh air. Breathing pure O₂ can give faster removal of CO

• Cyanide poisoning:
  • Cyanide inhibits the cytochrome oxidase enzyme of mitochondria
  • Two step treatment for cyanide poisoning:
    • 1) Give nitrites
      • Nitrites convert some hemoglobin to methemoglobin. Methemoglobin pulls cyanide away from mitochondria.
    • 2) Give thiosulfate.
      • Thiosulfate converts the cyanide to less poisonous thiocyanate.

The Parathyroid Glands

The parathyroid glands are 4 tiny structures embedded in the rear surface of the thyroid gland. They secrete parathyroid hormone (PTH) a polypeptide of 84 amino acids. PTH increases the concentration of Ca²⁺ in the blood in three ways. PTH promotes

• release of Ca²⁺ from the huge reservoir in the bones. (99% of the calcium in the body is incorporated in our bones.)
• reabsorption of Ca²⁺ from the fluid in the tubules in the kidneys
• absorption of Ca²⁺ from the contents of the intestine (this action is mediated by calcitriol, the active form of vitamin D.)

PTH also regulates the level of phosphate in the blood. Secretion of PTH reduces the efficiency with which phosphate is reclaimed in the proximal tubules of the kidney causing a drop in the phosphate concentration of the blood.

Hyperparathyroidism

Elevate the level of PTH causing a rise in the level of blood Ca²⁺ .Calcium may be withdrawn from the bones that they become brittle and break.

 Patients with this disorder have high levels of Ca²⁺ in their blood and excrete small amounts of Ca²⁺ in their urine. This causes hyperparathyroidism.

Hypoparathyroidism

This disorder have low levels of Ca²⁺ in their blood and excrete large amounts of Ca²⁺ in their urine.

DNA (Deoxyribonucleic acid) - controls cell function via transcription and translation (in other words, by controlling protein synthesis in a cell)

Transcription - DNA is used to produce mRNA

Translation - mRNA then moves from the nucleus into the cytoplasm & is used to produce a protein . requires mRNA, tRNA (transfer RNA), amino acids, & a ribosome

tRNA molecule

• sequence of amino acids in a protein is determined by sequence of codons (mRNA). Codons are 'read' by anticodons of tRNAs & tRNAs then 'deliver' their amino acid.
• Amino acids are linked together by peptide bonds (see diagram to the right)
• As mRNA slides through ribosome, codons are exposed in sequence & appropriate amino acids are delivered by tRNAs. The protein (or polypeptide) thus grows in length as more amino acids are delivered.
• The polypeptide chain then 'folds' in various ways to form a complex three-dimensional protein molecule that will serve either as a structural protein or an enzyme.

Hormones are carried by the blood throughout the entire body, yet they affect only certain cells.  The specific cells that respond to a given hormone have receptor sites for that hormone.  

This is sort of a lock and key mechanism.  If the key fits the lock, then the door will open.  If a hormone fits the receptor site, then there will be an effect.  If a hormone and a receptor site do not match, then there is no reaction.  All of the cells that have receptor sites for a given hormone make up the target tissue for that hormone.  In some cases, the target tissue is localized in a single gland or organ.  In other cases, the target tissue is diffuse and scattered throughout the body so that many areas are affected.  

Hormones bring about their characteristic effects on target cells by modifying cellular activity.  Cells in a target tissue have receptor sites for specific hormones.  Receptor sites may be located on the surface of the cell membrane or in the interior of the cell.

In general those protein hormones are unable to diffuse through the cell membrane and react with receptor sites on the surface of the cell.  The hormone receptor reaction on the cell membrane activates an enzyme within the membrane, called adenyl cyclase, which diffuses into the cytoplasm.  Within the cell, adenyl cyclase catalyzes or starts the process of removal of phosphates from ATP to produce cyclic adenosine monophosphate or c AMP.  This c AMP activates enzymes within the cytoplasm that alter or change the cellular activity.  The protein hormone, which reacts at the cell membrane, is called the first messenger.  c Amp that brings about the action attributed to the hormone is called the second messenger.  This type of action is relatively rapid because the precursors are already present and they just needed to be activated in some way.  

 Acute Obstructive Disorders
 1.    Heimlich maneuver
 2.    Bypass, tracheostomy w/catheter to suck up secretion

Blood Pressure

Blood moves through the arteries, arterioles, and capillaries because of the force created by the contraction of the ventricles.

Blood pressure in the arteries.

The surge of blood that occurs at each contraction is transmitted through the elastic walls of the entire arterial system where it can be detected as the pulse. Even during the brief interval when the heart is relaxed — called diastole — there is still pressure in the arteries. When the heart contracts — called systole — the pressure increases.

Blood pressure is expressed as two numbers, e.g., 120/80.

Blood pressure in the capillaries

The pressure of arterial blood is largely dissipated when the blood enters the capillaries. Capillaries are tiny vessels with a diameter just about that of a red blood cell (7.5 µm). Although the diameter of a single capillary is quite small, the number of capillaries supplied by a single arteriole is so great that the total cross-sectional area available for the flow of blood is increased. Therefore, the pressure of the blood as it enters the capillaries decreases.

Blood pressure in the veins

When blood leaves the capillaries and enters the venules and veins, little pressure remains to force it along. Blood in the veins below the heart is helped back up to the heart by the muscle pump. This is simply the squeezing effect of contracting muscles on the veins running through them. One-way flow to the heart is achieved by valves within the veins

Exchanges Between Blood and Cells

With rare exceptions, our blood does not come into direct contact with the cells it nourishes. As blood enters the capillaries surrounding a tissue space, a large fraction of it is filtered into the tissue space. It is this interstitial or extracellular fluid (ECF) that brings to cells all of their requirements and takes away their products. The number and distribution of capillaries is such that probably no cell is ever farther away than 50 µm from a capillary.

When blood enters the arteriole end of a capillary, it is still under pressure produced by the contraction of the ventricle. As a result of this pressure, a substantial amount of water and some plasma proteins filter through the walls of the capillaries into the tissue space.

Thus fluid, called interstitial fluid, is simply blood plasma minus most of the proteins. (It has the same composition and is formed in the same way as the nephric filtrate in kidneys.)

Interstitial fluid bathes the cells in the tissue space and substances in it can enter the cells by diffusion or active transport. Substances, like carbon dioxide, can diffuse out of cells and into the interstitial fluid.

Near the venous end of a capillary, the blood pressure is greatly reduced .Here another force comes into play. Although the composition of interstitial fluid is similar to that of blood plasma, it contains a smaller concentration of proteins than plasma and thus a somewhat greater concentration of water. This difference sets up an osmotic pressure. Although the osmotic pressure is small, it is greater than the blood pressure at the venous end of the capillary. Consequently, the fluid reenters the capillary here.

Control of the Capillary Beds

An adult human has been estimated to have some 60,000 miles of capillaries with a total surface area of some 800–1000 m². The total volume of this system is roughly 5 liters, the same as the total volume of blood. However, if the heart and major vessels are to be kept filled, all the capillaries cannot be filled at once. So a continual redirection of blood from organ to organ takes place in response to the changing needs of the body. During vigorous exercise, for example, capillary beds in the skeletal muscles open at the expense of those in the viscera. The reverse occurs after a heavy meal.

The walls of arterioles are encased in smooth muscle. Constriction of arterioles decreases blood flow into the capillary beds they supply while dilation has the opposite effect. In time of danger or other stress, for example, the arterioles supplying the skeletal muscles will be dilated while the bore of those supplying the digestive organs will decrease. These actions are carried out by

• the autonomic nervous system.
• local controls in the capillary beds