pt 2 RAT 2

Thyroxine (T4)

- A hormone produced by the thyroid gland that contains four iodine atoms, less active form of the hormone which can be converted into T3 by cells when needed

List three ways that parathyroid hormone raises blood calcium levels.

1. Increasing release of calcium ions from bone stimulating osteoclasts. Enhances osteoclasts which are bone destroying cells and they release calcium ions into the blood by breaking down the extracellular matric of the bone 2. Increasing absorption of dietary calcium ions by the small intestine. PTH acts indirectly as they involve vitamin D. PTH acts on the kidneys to stimulate the conversion of Vitamin D to its active form, vitamin D3 or calcitriol. In this form, calcitriol increases the number of calcium ions absorbed from the small intestine 3. Increasing reabsorption of calcium ions from the fluid in the kidneys. PTH acts on the kidney tubule cells to increase the number of calcium ions reclaimed from the fluid in the tubules before it becomes urine and is lost to the body

What are the effects of thyroid hormone?

1. Regulation of the metabolic rate and thermoregulation- set the basal metabolic rate (energy expenditure at rest) by increasing the synthesis of ATP-requiring sodium potassium pumps, triggering gluconeogenesis in the liver, break down of proteins, and the building of proteins and fats. Increasing the rate at which cells carry out both catabolic and anabolic reactions, no net change essentially occurs 2. Promotion of growth and development- thyroid hormones are required for bone, muscle, and nervous system growth 3. Synergism with the sympathetic nervous system- Elevations in thyroid hormones act on target cells of the sympathetic nervous system and increase the production of receptors for sympathetic nervous system

Triiodothyronine

A hormone produced by the thyroid gland that contains three iodine atoms; form of the hormone that has higher physiological activity in promoting growth and development, regulating the metabolic rate and heat production, and promoting the effects of the sympathetic nervous system on its target cells

What are the names of the two forms of thyroid hormone? Collectively, these two forms are called thyroid hormone.

Triiodothyronine and Thyroxine · These are amino acid hormones, however they are nonpolar and hydrophobic, so they do not bind to cell surface receptor proteins, they act like steroid hormones and activate or inhibit the transcription of certain genes

What are the three branches that arise from the arch of the aorta?

o Brachiocephalic artery- the first branch off the aortic arch, branches off into the right common carotid artery that supplies the right side of the head and neck and the right subclavian artery that supplies the right upper limb and thorax o Left common carotid artery- the middle branch of the aortic arch which supplies the left side of the head and neck o Left subclavian artery which supplies the left upper limb and thorax

Remember matrix from the tissues chapter? What is the matrix of blood called?

plasma

About how many months is the average lifespan of an RBC?

· 100-120 days, they are under high pressure and lack the cellular machinery to repair damage

How many parathyroid glands are typically found in humans?

· 3-5 with 4 being the most common

How many molecules of oxygen can each hemoglobin molecule bind?

· 4, one for each subunit · The more oxygen bound to hemoglobin, the more bright red it is, the less it becomes more red-purple and dark

How much blood does a typical person have?

· 5 liters · Connective tissue

Describe the structure of hemoglobin.

· A large protein that consists of four polypeptide subunits: two alpha chains and two beta chains · Each polypeptide is bound to an iron-containing compound called a heme group · The heme binds to oxygen in parts of the body where oxygen levels are high forming a structure called oxyhemoglobin

What is plasma?

· A pale yellow liquid that consists primarily of water

Name and describe some important plasma proteins.

· Albumin- the most abundant plasma protein, largely responsible for the plasma's colloid osmotic pressure, or the pressure that draws water into the blood via osmosis · Immune proteins/antibodies- plasma proteins of the immune system. Are produced by leukocytes · Transport proteins- hydrophilic and can associate with water molecules and aid in transport of hydrophobic molecules · Clotting proteins

What are the four divisions of the aorta?

· Ascending aorta- the initial segment of the aorta which travels superiorly · Aortic arch- the ascending aorta curves to the left to become the aortic arch which gives off three large arteries · Descending thoracic aorta- the aortic arch turns inferiorly to become the descending thoracic aorta which travels through the mediastinum and supplies thoracic structures · Descending abdominal aorta- the descending thoracic aorta pierces the diaphragm and enters the abdominopelvic cavity to become the descending abdominal aorta, whose branches supply the abdominal viscera

What are the two terminal branches of the aorta? Be able to label these arteries.

· At about the level of the fourth lumbar vertebra, it splits into its terminal branches, the right and left common iliac arteries. These arteries then split into the internal iliac arteries, which supply pelvic structures and external iliac arteries, which supply the lower limbs

What cells are found between follicles? What do they produce?

· Between the thyroid follicles lie clusters of parafollicular cells. These cells are larger than follicle cells, and they produce the hormone calcitonin

Describe the shape of an erythrocyte or red blood cell (RBC).

· Biconcave disc · Gives it a large surface to volume ratio which is critical for gas exchange

This by-product of heme is sent to the liver for excretion. What is it?

· Bilirubin is sent to the liver for excretion, where it is modified and excreted in feces and urine

What cells produce calcitonin?

· Calcitonin is produced by the thyroid gland's parafollicular cells · Calcitonin decreases the blood calcium level, its' primary action includes inhibiting the activity of the osteoclasts in bone. This leaves the effects of the osteoblasts, the "bone building" cells unopposed. Osteoblasts deposit calcium ions into the bone, which reduces the blood concentration of calcium ions

Why is exposure to CO lethal?

· Carbon monoxide binds to hemoglobin more strongly than does oxygen and has an affinity for hemoglobin about 200 times greater than that of oxygen. CO also changes the shape of hemoglobin so that the oxygen already bound to hemoglobin cannot be released into the tissues. This makes exposure to a high level of CO lethal, it severely decreases the oxygenation of body tissues

Why is the hematocrit generally higher in males?

· Due to the males' typically larger body size and greater muscle and bone mass

What hormone is needed for erythrocyte differentiation?

· Erythrocyte CFUs next differentiate into proerythroblasts, a process requiring the hormone erythropoietin or EPO, secreted from the kidneys · Erythropoietin- the hormone produced by the kidneys that increases the rate of erythrocyte production and decreases the time it takes for them to mature`

What are the three types of formed elements?

· Erythrocytes or red blood cells · Leukocytes or white blood cells · platelets

What are the functions of blood?

· Exchanging gases- oxygen is transported from the lungs to the tissues primarily by erythrocytes, erythrocytes and plasma also transport CO2 away from the tissues to the blood · Distributing solutes- plasma transports many solutes, including nutrients, hormones and wastes as well as ions. Key in regulating ion concentration · Performing immune functions- Both the leukocytes and proteins of the immune system use blood as a transport vehicle to reach tissues in the body · Sealing damaged vessels by forming blood clots- platelets and certain proteins form a blood clot to prevent excessive blood loss · Preserving acid-base homeostasis- The pH stays fairly constant because blood composition controls many of the body's most important buffer systems · Stabilizing blood pressure- blood volume is a main determinant of blood pressure

Mature RBC's lack most organelles and are anucleate. What does that mean?

· Have no nucleus · Means they are not able to carry out oxidative catabolism or protein synthesis

What happens to the protein part of hemoglobin?

· Hemoglobin is broken down into amino acids, iron ions and bilirubin. The polypeptide chains of hemoglobin are broken down into amino acids, the iron ions are removed and the reaminder of the heme is converted into the waste product biliverdin and then to bilirubin. Green and yellow bruising

There are about a billion molecules of which protein in RBC's? What is the function of this protein?

· Hemoglobin- the iron containing protein in erythrocytes that binds and carries oxygen throughout the blood

What stimulates the release of calcitonin?

· Hypercalcemia occurs when the calcium ion level in the blood increases above normal. In response to this, calcitonin is released

Too few RBC's?

· If the hemocrit drops too low, there will not be enough erythrocytes available to transport oxygen to the tissues

Erythropoiesis must be regulated so that there are not too many or too few RBC's. What happens if there are too many RBC's?

· If the hemocrit is too high, the blood becomes thicker as its viscosity increases, making blood flow sluggish

What happens to the heme part of hemoglobin?

· Iron ions and amino acids are recycled and used to make new hemoglobin in red bone marrow. Most of the iron ions and amino acids are transported to the red bone marrow to be incorporated into new hemoglobin.

What detects falling oxygen levels?

· Kidney cells detect a low oxygen level. They act as chemoreceptors and monitor the blood's oxygen content

How does it respond?

· Kidneys produce more erythropoietin and release it into the blood. Erythropoietin communicates with HSCs in the bone marrow

What are plasma proteins?

· Make up about 9% of plasma volume. Are too large to fully dissolve in the water portion, so they form a colloid

What composes the thyroid gland?

· Microscopically the thyroid gland is composed of multiple spheres known as thyroid follicles in which thyroid hormones are produced and stored.

Most of the formed elements arise from the same early stem cell. What is the name of this stem cell? Where is it found?

· Occurs in red bone marrow which houses hematopoietic stem cells

What is the primary target of calcitonin?

· Osteoclast inhibitor

What is the primary function of erythrocytes?

· Oxygen and carbon dioxide transport

What stimulates the release of parathyroid hormone?

· PTH is secreted in response to a declining blood calcium ion concentration, hypocalcemia, · PTH is a peptide hormone that increases the concentration of calcium ions in the extracellular fluid

What are the two main components of blood?

· Plasma- the fluid extracellular matrix of blood, consists of water, proteins and dissolved solutes · Formed elements- the cells ad cell fragments that are suspended in plasma

How does this help restore the oxygen levels?

· Production of erythrocytes increases. It speeds up the rate of erythropoiesis and reduces the amount of time needed for new erythrocytes to mature. Can also trigger replacement of yellow marrow with red marrow

What cell lacks a nucleus and ejects organelles before entering the bloodstream in the bone marrow? What does this cell differentiate into?

· Proerythroblasts develop into erythroblasts, which rapidly synthesize hemoglobin and other proteins. As erythroblasts mature, their nuclei shrink and are eventually ejected from the cells, at which poin they are called reticulocytes · These cells retain some organelles like ribosomes, when they eject the remaining organelles by exocytosis they enter the bloodstream by squeezing through the large pores in the sinusoidal capillaries of the bone marrow, and are now considered erythrocytes. Takes 5-7 days

How is thyroid hormone production regulated?

· Regulated by a negative feedback loop that has multiple tiers of control. · Hypothalamic neurons secrete TRH at a fairly constant rate, TRH then travels to the anterior pituitary via the hypothalamic-hypophyseal portal system and stimulates the production and release of TSH. TSH stimulates multiple responses from the thyroid including o Production of T3 and T4 by follicle cells o Secretion of T3 and T4 from follicle cells into the blood o Growth and development of the thyroid · Secretion of both TRH and TSH is inhibited by rising levels of free T3 and T4

What cells engulf old RBC's that become stuck in sinusoids in the spleen?

· Spleen macrophages digest erythrocytes

Regulation of Erythropoiesis

· Stimulus: The blood oxygen level decreases below normal range. A decrease in the oxygen content of blood is usually due to respiratory problems, but it may also result from heart conditions or reduced availability of oxygen (e.g., at high altitudes). · Receptor: Kidney cells detect a low oxygen level. Specialized cells in the kidneys act as chemoreceptors and monitor the blood's oxygen content. They are stimulated when the oxygen content falls below a certain level. · Control center: Kidneys produce more erythropoietin and release it into the blood. The kidneys produce erythropoietin, which communicates with HSCs in the bone marrow. Here we see an example of the Cell-Cell Communication Core Principle (p. 28). · Effector/response: Production of erythrocytes increases. Erythropoietin has many effects. It speeds up the rate of erythropoiesis and reduces the amount of time needed for new erythrocytes to mature. Erythropoietin can also trigger the replacement of yellow bone marrow with red bone marrow. · Homeostasis: The blood level of oxygen rises to normal. As more erythrocytes enter the blood, the hematocrit and oxygen-carrying capacity of the blood increase. Under normal circumstances, the oxygen content of blood will rise as a result. Chemoreceptors in the kidneys detect that the oxygen level has returned to normal, and erythropoietin production and release decline to normal.

Regulation of Calcium Ion Homeostasis

· Stimulus: blood calcium ion concentration decreases below the normal range · Receptor: chief cells in the Parathyroid gland detect the low calcium ion level · Control: the chief cells increase PTH secretion · Effector/response: the effects of PTH on target cells increase the blood calcium ion concentration · Homeostatic range and negative feedback: as the blood calcium ion level returns to the normal range, negative feedback to chief cells decreases PTH secretion

How does plasma impact the viscosity of blood?

· The amount of water in plasma is one factor that determines the thickness or viscosity of blood. If plasma contains less water, its viscosity increases and blood flow becomes sluggish

What is the largest artery in the body?

· The aorta- arises from the left ventricle and delivers blood to the systemic circuit · This artery carries newly oxygenated blood from the heart for delivery to the body.`

Describe the shape of the thyroid gland. What is the isthmus?

· The butterfly shaped thyroid gland consists of right and left lobes connected by a small band called the isthmus.

What cells form the border of follicles? What do they produce?

· The follicles are bounded by a layer of simple cuboidal epithelial cells referred to as follicle cells which produce thyroid hormones

What cells in the parathyroid gland produce hormone? What hormone do they produce?

· The hormone secreting cells of the parathyroid gland, which produce parathyroid hormone, are called chief cells

What is found inside a follicle? What does it contain?

· The interior follicle is filled with colloid, a protein rich, gelatinous material where the precursor to thyroid hormone is stored. Colloid also contains a high concentration of iodine atoms which are required for thyroid hormone synthesis

Which parts of the hemoglobin molecule are recycled?

· The iron ions are transferred to a protein called transferrin that carries them through the blood.

Where are most plasma proteins produced?

· The liver

Where are the parathyroid glands located?

· The parathyroid glands are small glands embedded in the posterior surface of the thyroid gland

What is the hematocrit? How is it measured?

· The portion of the blood that consists of erythrocytes

What is erythropoiesis?

· The process of differentiation and maturation of erythrocytes · Begins when HSCs differentiate into progenitor cells called erythrocyte colony forming units and are committed · 250 billion cells per day

What is hematopoiesis?

· The process of differentiation and maturation of the formed elements of blood · Occurs in red bone marrow which houses hematopoietic stem cells

Many RBC's die in this organ that has been called the RBC graveyard. What is it?

· The spleen, RBC's have a hard time making passage in the sinusoids, tiny capillaries of the spleen

Where is the thyroid gland located?

· The thyroid gland is found in the anterior neck, just superficial to the larynx.

What layers appear if a sample of blood is centrifuged? What is found in each layer?

· The top layer is plasma, which constitutes 55% of the total blood volume · The middle is the buffy coat, which makes up 1% of the total blood volume. Consists of leukocytes and platelets · The bottom layer, 44%, is dark red and contains erythrocytes, called hematocrit

What is deoxyhemoglobin? Carbaminohemoglobin? Carboxyhemoglobin?

· Where the oxygen level is low, hemoglobin releases the oxygen and becomes deoxyhemoglobin · In venous blood where the oxygen level is low, hemoglobin binds to CO2 to form carbaminohemoglobin. · Hemoglobin also binds to carbon monoxide to form carboxyhemoglobin

What is hemoglobin called when oxygen is attached?

· oxyhemoglobin

The first branch gives rise to which two arteries?

· the first branch off the aortic arch, branches off into the right common carotid artery that supplies the right side of the head and neck and the right subclavian artery that supplies the right upper limb and thorax