BIO 202: Chapter 1.3 - 1.5 Endocrine System Histology, Feedback Loops, and Blood

thyroid gland

parafollicular cells

large, pale stained cells between or adjacent to the follicles

follicle cells

form a ring of simple cuboidal epithelium that surround the colloid

adrenal gland

adrenal capsule

extremely thin and is the outermost layer

adrenal cortex

deep to the capsule and is made up of three distinct zones

zona glomerulosa

thin outer zone, cells arranged in small, round clusters nearest to the adrenal capsule

zona fasciculate

thick middle zone, lightly stained cells stacked in columns, foamy or sponge like cytoplasm

zona reticularis

thin inner zone, darkly stained, tightly packed cells in net like pattern

adrenal medulla

innermost region with numerous, loosely arranged blood vessels and clusters of hormone secreting cells

pancreas

pancreatic ducts

endocrine pancreatic islets

lighter in color, slightly cuboidal, arranged around a duct

exocrine pancreatic acinar cells

no distinct arrangement, may be larger, stain free spaces between them

negative feedback loop

automatic stabilizing mechanism in which hormones are released into bloodstream to act on target cells to correct disturbance to restore homeostasis, decrease gland activity, and decrease hormone concentration

thyroid hormone regulation

1. hypothalamus releases thyrotropin releasing hormone and stimulates anterior pituitary to release thyroid stimulating hormone

2. thyroid stimulating hormone stimulate thyroid gland to secrete T3 and T4

3. T3 and T4 levels rise in blood and inhibit thyrotropin and thyroid stimulating hormone

4. overproduction of thyroid hormones is prevented

cortisol regulation

1. hypothalamus releases corticotropin releasing hormone and stimulates the anterior pituitary to release adrenocorticotropic hormone

2. adrenocorticotropic hormone stimulates the adrenal cortex to release cortisol

3. elevated cortisol levels inhibit corticotropin and adrenocorticotropic release

4. further cortisol production is reduced

blood glucose regulation

1. blood glucose levels fall and pancreas releases glucagon which stimulates glycogen breakdown in the liver

2. blood glucose levels rise and pancreas releases insulin which promotes glucose uptake by cells

3. blood glucose levels return to normal and hormone secretion decreases

positive feedback loops

response that amplifies original stimulus to accelerate a process until an outcome is reached

childbirth

cervical stretching stimulates the release of oxytocin which causes stronger uterine contractions to further stretch the cervix more until baby is delivered

blood clotting

in a damaged vessel, platelets stick to injury site and release chemicals that attract more platelets that further release more chemicals until clot fully seals break

thermostat

negative feedback is like a _____ that works to bring the temperature back to normal

microphone

positive feedback is like a _____ that works to amplify a signal until a specific result is reached

viscosity

the resistance of a fluid to flow, caused by the cohesion between its particles

• aka the thickness and stickiness of a fluid

4.5 to 5.5

blood is ____ times more viscous than water

osmolarity

total concentration of dissolved particles that cannot pass through the blood vessel wall

• helps blood regulate fluid movement between blood and tissues

plasma and formed elements

two main components of whole blood

plasma

clear, light-yellow fluid portion of blood

• 55% of volume of whole blood

• consists primary of water, proteins, nitrogenous wastes, hormones, gases, and other solutes

albumin

smallest and most abundant plasma protein that transports solutes and buffers plasma pH

• major contributor to blood viscosity and osmolarity

globulin

plasma protein that plays role in solute transport, clotting, and immunity

fibrinogen

plasma protein that is a soluble precursor of fibrin which is a sticky protein that forms framework of blood clots

serum

fluid that remains after blood clots and solids are removed

• identical to plasma but lacks fibrinogen

formed elements

cellular portion of blood

• accounts for 45% of volume of whole blood

• includes erythrocytes, thrombocytes, and leukocytes

erythrocytes

red blood cells that function to carry oxygen throughout the body using hemoglobin and to pick up carbon dioxide from tissues and unload it in the lungs

• most numerous blood cells with average of 44% of total blood volume

• reddish-pink color, biconcave shape, absent nucleus and most organelles

hemoglobin

iron-containing protein and red pigment that gives blood its color

hematocrit

packed cell volume

• 40 to 50% in males

• 36 to 44% in females

erythropoiesis

erythrocytes production which occurs in red bone marrow and takes 3 to 5 days

erythropoietin

hormone that stimulates the process of erythropoiesis

anemia

low hematocrit which may cause fatigue, weakness, and shortness of breath

polycythemia

high hematocrit which can increase blood viscosity and raise risk of clotting and stroke

high, lower

at ___ altitudes, oxygen levels are ___ so kidneys release more erthyropoietin and increase RBC productions to improve oxygen delivery

blood doping

a performance-enhancing method where athletes artificially increase red blood cell count to boost oxygen delivery to muscle to improve endurance

thrombocytes

platelets that function in hemostasis by forming platelet plugs and the initiating blood clotting process

• make up less than 1% of total blood volume

• not true cells, lack nucleus and most organelles

• circulate for 5 to 6 days before removed by spleen or liver

hemostasis

process of stopping bleeding

megakaryocytes

extremely large bone marrow cells with multiobed nuclei from which thrombocytes originate from

thrombopoietin

hormone that stimulates thrombocyte production in red bone marrow

clotting cascade

chain reaction of chemical events involving clotting factors that lead to the conversion of fibrinogen into fibrin to form a stable clot

clotting cascade step 1

vascular spasm: damaged blood vessel immediately constricts to slow down blood loss

clotting cascade step 2

platelet plug formation: platelets stick to exposed collagen fibers in the vessel wall and clump together to form temporary plug to cover injury

clotting cascade step 3

coagulation cascade activation: a chain reaction of clotting proteins begins

• intrinsic pathway: triggered by damage inside a vessel

• extrinsic pathway: triggered by damage to tissue outside the vessel

clotting cascade step 4

common pathway: both intrinsic and extrinsic pathways join together at a specific point called the activating factor X that leads to production of thrombin that converts fibrinogen into fibrin

clotting cascade step 5

stable clot formation: fibrin forms a mesh that traps blood cells to create a strong and stable clot to fully seal injury

partial thromboplastin time

clotting test that measures the intrinsic and common pathways and is used to monitor heparin therapy

prothrombin time

clotting test that measures the extrinsic and common pathways

international normalized ratio

clotting test used to monitor warfarin (coumadin) therapy

thrombocytopenia

low thrombocytes which can lead to easy bruising, prolonged bleeding after injury, and spontaneous internal bleeding

thrombocytosis

high thrombocytes which may result in bone marrow disorders, chronic inflammation, and can increase risk of abnormal blood clot formation, stroke, and heart attack

leukocytes

white blood cells that function to protect the body against infection, disease, and foreign invaders as part of the immune system

• make up less than 1% of total blood volume

• have nucleus and other organelles

• classified into two main groups based on presence or absence of visible cytoplasmic granules when stained

granulocytes

neutrophils, eosinophils, and basophils

neutrophils

function as first responders to infection by ingesting and destroying bacteria and cellular debris using enzymes and antimicrobial chemicals

• most numerous leukocyte, making up 60 to 70% of total white blood cells

• low levels indicate bone marrow suppression or severe infection

eosinophils

function to attack parasitic worms, participate in allergic reactions, and help regulate inflammation by phagocytizing antigen-antibody complexes

• make up about 2 to 4% of total white blood cells

• elevated in parasitic infections, allergies, autoimmune diseases, and certain skin disorders

basophils

function to release histamine and other inflammatory mediators when activated to contribute to allergy symptoms like swelling, redness, and itching and to release heparin to prevent clotting

• least numerous white blood cells, making up less than 1% of total count

• elevated in allergic reactions, hypothyroidism, and certain chronic inflammatory conditions

lymphocytes

function in adaptive immunity

• make up about 20 to 25% of total white blood cells

• elevated in viral infections and some chronic bacterial infections

• low levels may occur in immune deficiencies or after chemotherapy

B lymphocytes

produce antibodies that bind to antigens

T lymphocytes

enhance other immune responses, destroy cancer cells, and kill virus-infected cells

monocytes

function to present antigens to lymphocytes to active the immune response and mature into macrophages which are active phagocytes that engulf bacteria, dead cells, and debris

• largest sized white blood cell, make up 3 to 8% of total white blood cells

• elevated in viral infections, chronic inflammation, and certain leukemias

leukocytosis

higher than normal white blood cell count

• often indicates infection, inflammation, tissue injury, or leukemia

leukopenia

lower than normal white blood cell count

• can result from bone marrow failure, autoimmune disorders, viral infections, or chemotherapy