Biology 2404 A&P Basics Lab Exercise Endocrine System Dr. Weis
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Students should be able to
* define hormone and describe hormone composition and regulation
* Name the hormones from the Pituitary gland
* Name the classical endocrine glands, their hormones, and function(s)
* Name organs or tissues that have secondary endocrine functions, their hormone secreted and its effects
* Define related terms, such as feedback, homeostasis
Read related material in textbook
The endocrine system is composed of neural and epithelial glandular tissues that help integrate responses to provide most of the overall body control. Since endocrine glands are ductless, most of their secretions are put into the bloodstream to allow for distribution to target organs. These chemicals called hormones help the body’s long term control for homeostasis. This control is primarily accomplished by negative feedback mechanisms, although a few positive feedback mechanisms are in place.
Hormones
Hormones are chemicals secreted in response to various stimuli.
The three stimuli for secretion are:
Hormonal one hormone stimulates the release of another hormone
Humoral blood plasma levels of a substance stimulates release of a hormone
Neural neuron secretions stimulates release of a hormone
Hormones may interact with other hormones to cause synergistic effects, antagonize the effects of another hormone, or give permission for release of other hormones. These interactions result from the chemical structure of the hormone and the hormone binding to the receptor site at the target organ.
Hormones can be divided into three chemical categories:
1) Amino Acid single amino acid that is modified
short chain amino acid, also called a peptide
long chain amino acid called a polypeptide or protein
2) Steroids based on cholesterol
3) Eiconosoids based on Fatty acids
The chemical structure determines the solubility and how & where the hormone interacts with its receptor. Amino acid based hormones are primarily water soluble. There are a few exceptions with some of the single amino acid based hormones which act like a fat soluble substance. The hormones based on fats such as cholesterol or fatty acids are fat soluble only.
The importance of solubility occurs at the cell membrane of the target organ. Recall that the cell membrane is a phospholipid bilayer with proteins located in and on the membrane. Phospholipids belong to the lipid class of fatty organic macromolecules, since they are based on fatty acids.
The large, water soluble hormones can not get through the fatty phospholipid layers of the target organs cell membrane. These hormones are also too large to use the channel or carrier proteins embedded in the cell membrane. In order to signal the cell, the hormone binds to proteins on the periphery of the membrane. These peripheral proteins are tied to an enzyme cascade that will signal the cell by way of formation of internal secondary messengers. Hormones that must use the secondary messenger signal transduction are the peptides, proteins, and most modified single amino acids.
Fat soluble hormones and those that have fat soluble properties can cross the fatty phospholipid membrane, so their receptors are located within the cell. Ultimately, the signal will cause the DNA to undergo various processes. This transduction signaling can be termed Direct DNA activation.
The hormone binding to its receptor will trigger the formation of a receptor-hormone complex (HRC). The HRC is the trigger to signal the cell. Examples of cell responses can be changes in ion permeability by opening or closing ion channels, initiating enzyme production, triggering cell division, or synthesis of another hormone.
Hormones can turn on or turn off a process depending on the receptor and its enzyme interactions.
Since hormones travel primarily by the plasma to their target organs, their blood levels can be measured. The length of time a hormone is in circulation varies, but for most it is minutes to hours. The liver and kidney are responsible for removing hormones from circulation. Tests can be done to determine if a hormone feedback response is working properly.
Endocrine System
Endocrine glands and tissues can be divided into two groups:
Classical Endocrine glands that function to only secrete hormones
Secondary endocrine organs / tissues whose primary function involves something other than hormone secretion, but can secrete hormones when needed
Examples of the classical endocrine glands are the pituitary, pineal, parathyroid, thyroid, thymus, and adrenal gland.
Examples of secondary endocrine organs / tissues are the hypothalamus, pancreas, gastrointestinal tract, heart, kidney, and reproductive organs such as the testes, ovaries, and placenta.
The pituitary or hypophysis has three regions based on body plane references.
The three regions are the anterior pituitary, posterior pituitary, and intermediate pituitary. Hormones released from these regions are under the control of the hypothalamus.
The posterior pituitary (PP) is actually a neural tissue extension of the hypothalamus and it forms the telodendria and synaptic knobs with supporting cells. The posterior pituitary is also called the neurohypophysis. When the cell bodies in certain hypothalamic regions are stimulated, it triggers release of one of two hormones.
These hormones were initially made in the hypothalamus and stored in the posterior pituitary. The two hormones are amino acid peptide based, with very similar structure, but different target organs.
The hormones of the Posterior Pituitary are:
OT oxytocin that binds to estrogen sensitive smooth muscle of the uterus for labor,
and mammary gland for milk ejection.
ADH anitdiuretic hormone that binds to renal tubules to signal the reabsorption of water
The anterior pituitary (AP) is an epithelial glandular tissue whose alternate name is the adenohypophysis. In designated regions, the hypothalamus will secrete hormones into the blood supply of the anterior pituitary. This specialized blood supply is called the hypophyseal portal system. These releasing or inhibitory hormones from the hypothalamus will have its effects on one of the three epithelial cell types found in the anterior pituitary. As a result, the hypothalamus signals the anterior pituitary to release one of six hormones into the general circulation.
The six anterior pituitary (AP) hormones are:
ACTH Adrenocorticotrophic Hormone
Target organ is the adrenal cortex middle and inner layers
Function is to stimulate release of cortisol hormones
GH Growth Hormone
Target organ is most all body organs
Function in children is to stimulate growth and development
Function in adults is to promote repair and replacement
FSH Follicle Stimulating Hormone
Target organ is the reproductive tissues that produce gametes
Function in females is development of follicles with oocytes
Function in males is the development of sperm
LH Lutenizing Hormone
Target organ is the reproductive organs
Function in females is to cause ovulation and development of a Corpus Luteum
(CL) that produces progesterone
Function in males is to promote production of testosterone
PRL Prolactin
Target organ is the mammary glandular tissue
Function is to promote milk production
TSH Thyroid Stimulating Hormone
Target organ is the thyroid
Function is to stimulate the thyroid to release T3, T4
The intermediate pituitary (IP) is much like the glandular tissue found in the anterior pituitary. In humans, it is less developed and appears to resemble connective tissue, while in some mammals it forms ¼ to 1/3 of the pituitary size. In most mammals the hypothalamus controls the IP much the same way as the AP, while in humans it is thought that ACTH plays a role in control. The hormone from the IP is MSH.
Melanocyte Stimulating hormone’s known target organ is the melanocytes of the skin. With changes in the light cycle, it can promote color change in some animals.
Drawing: Hypothalamus and Pituitary
Histology
Pineal
The pineal gland is neural tissue located in the roof of the third ventricle in the region of the epithalamus of the diencephalon. This area of the brain was once called the “eye” brain because light entering the eye will affect this brain region to regulate sleep wake cycles. The hormone released in response to different light levels is melatonin. In darkness, melatonin levels rise to help regulate the sleep cycle, while light causes the hormone to breakdown. The amount of light present in the four seasons can affect the levels of melatonin in control of their reproductive cycles, mating, and migratory behavior.
Drug bottle with label
Parathyroid
The parathyroid is embedded in the dorsal surface of the thyroid gland. In most mammals, there are two pairs (4) of glands. The chief cells of this gland secrete the hormone PTH, parathyroid hormone or Parathormone. Regulation of secretion is based on blood (humoral) levels of calcium (Ca++). In response to low blood calcium levels, the chief cells release PTH into the blood. Target organs are the osteoclasts that are signaled to digest bone and release calcium into the blood; and the kidney juxtaglomerular apparatus is signaled to make calcitrol from vitamin D.
Calcitrol then signals the kidney tubules to reabsorb calcium and signals the gastrointestinal track to absorb calcium from the diet. All target organs involve the retrieval of calcium and the restoration of blood calcium levels.
Thyroid
The thyroid is located in the ventral neck and has the appearance of a bow tie with two lobes connected by a band called the isthmus. Microscopically the thyroid has follicles and extrafollicular cells. The cuboidal cells of the follicles use iodine and the amino acid tyrosine to make the two thyroid hormones, T3 or triiodothyronine and T4 called thyroxine. The number subscript 3 and 4 indicate the number of iodine molecules attached to tyrosine. These thyroid hormones are stored bound to proteins in the follicular fluid of the thyroid follicles. The thyroid gland can store enough thyroid hormone for approximately 30 days. Stimulation for T3 and T4 release comes from the AP-TSH which is under the influence of the hypothalamic thyroid releasing hormone, TRH.
T3 is the active hormone, but is short lived, so in order to have thyroid hormone reach target organs throughout the body, T4 is primarily released. T4 is the non active form of the hormone and can travel bound to blood proteins. At the cell membrane of the target organ, T4 is converted to T3. T3 receptors are internal since the hormone acts as if it were fat soluble. The receptors in the cell are found on the mitochondria and certain regions of DNA to trigger enzyme production. Together, these effects control the metabolic rate of the body and how carbohydrates, proteins and fats are converted to energy. Thyroid hormones work with growth hormone and liver hormones that are also needed for normal growth and development, especially for proper nervous system maturation.
The clusters of extrafollicular cells that surround the thyroid follicles are called the parafollicular cells or “C” cells. These glandular cuboidal clumps of cells secrete the hormone Calcitonin. Control of secretion is under humoral stimulus reflecting blood levels of Ca++. In response to high blood calcium levels, the “C” cells secrete Calcitonin, whose target organ is the bone osteoblasts. Osteoblasts will take the calcium from the blood plasma to store and build bone. Calcitonin also signals the kidneys to excrete calcium and phosphate into the urine. Calcitonins effects are to lower blood calcium by storing calcium in bone or secreting it into the urine for elimination.
Blood calcium plasma levels are kept at a homeostatic range between 9-10 mg/dl.
The control of blood calcium comes from the interaction between PTH from the parathyroid gland and Calcitonin from the “C” cells of the thyroid.
Histology:
Thymus
The thymus in humans is a bi-lobed, triangular reticular connective tissue with cuboidal epithelial cells. The thymic histological regions are the capsule, cortex, and medulla. The reticular connective tissue allows for support of the white blood cells found throughout the organ. Because these WBCs form the majority of the specific immune defenses, the thymus is considered to be a primary immune organ. The immature lymphocytes that migrate to the thymic cortex will undergo structural changes under hormonal influence from specialized cells in the medulla. These hormones are collectively known as thymosins and function to help program these lymphocytes to become Thymic lymphocytes or T-lymphocytes called T-cells.
The adrenal gland is a small, triangular organ that sits near or on the superior lobe of each of the kidneys. The histological regions of the adrenal gland are the capsule, cortex, and medulla. The capsule is fibrous connective tissue that helps anchor the adrenal gland to the abdominal wall and surrounding structures. The cortex consists of glandular epithelial cells whereas the medulla is composed of nervous tissue that is part of the sympathetic autonomic nervous system (ANS).
The adrenal cortex is divided into three zones that secrete various hormones. These are:
a) Zona Glomerulosa small band of cells under the capsule in a circular pattern secretes
mineralocorticoids that regulate ions (minerals). The primary hormone is
aldosterone that regulates sodium. The target organ is the kidney tubules
to signal the reabsorption of Na+.
b) Zona Fasciculata middle, larger area of the cortex in a long band pattern secretes glucocorticoids
such as cortisol, hydrocortisone. Target organs are most of the body tissues with
receptors. Hormone functions to change carbohydrate and fat metabolism and
to help stabilize cell membranes and slow the immune response.
c) Zona Reticularis inner layer of cortex in a meshwork like pattern secretes glucocorticoids
and gonadocorticoids such as testosterone.
Target organs are most body tissues with the appropriate receptors.
Functions as above and the gonadocorticoids help with sex drive
(testosterone) and estrogens.
The adrenal medulla is a postganglionic sympathetic neuron. This neuron will make norepinephrine (20%) and epinephrine (80%) and store these neurotransmitters in the synaptic knob like other neurons. The difference is that these chemicals are released into the blood stream instead of the synaptic cleft. These neurohormones are under neural control and help to provide the flight / fight / freeze response of the ANS sympathetic division.
Adrenal Histology : Adrenal cortex, Adrenal Medulla
Drug photos: Epinephrine, ACTH, Aldosterone, Dexamethasone, Prednisone, Depo-Medrol
Secondary Endocrine Glands / Tissues
Pancreas
The pancreas is a tongue shaped organ that lies below (inferior) to the stomach.
The primary function of the pancreas is to secrete digestive enzymes to continue chemical digestion that aids in absorption of nutrients. These digestive enzymes come from the exocrine (acinar) pancreas and travel through ducts to reach the small intestine. The endocrine pancreas are several clusters of cells known as the Islets of Langerhans.
Several cell types make up the pancreatic islets and function to secrete various hormones.
These are:
Alpha cells ά Hormone = glucagons Target organ = liver
Function is to increase blood sugar levels
Beta cells β Hormone = insulin Target organ = most tissues
Function is to decrease blood sugar levels and allow
Glucose to enter most cells. Tissues that DO NOT
Require insulin are the brain, RBCs, GI tract, and kidneys.
Delta cells Δ Hormone = somatostatin Target organ is pancreas
Function is to stop the release of hormones from the alpha and beta cells.
F cells Hormone = pancreatic peptide Target organ is the GI tract to aid in secretion of digestive enzymes.
Blood glucose level: Normal Range is 70-125 mg /dL
Reproductive organs
Testes and Ovaries primary function is to form sex cells or gametes. Their secondary function is to secrete the reproductive hormones that aid in gamete formation and create visible secondary sex characteristics.
Testes Testosterone from the interstitial (Leydig) cells
Ovaries Estrogens: Estradiol, Estrone,
Progestins: Progesterone
Androgens: Testosterone
Relaxin
Inhibin
Reproductive Models : Male, Female
Reproductive Drugs : Estradiol, Lutalyse (PGF2alpha)
Other Secondary Endocrine Glands / Tissues
Organ Primary Function Hormone Function
Stomach digestion Intrinsic Factor Stimulate B12 absorption
Gastrin stomach motility
Duodenum absorption CCK release of bile from gall bladder
Secretin stimulates pancreatic release
of bicarbonate rich secretion
Liver detoxify Somatomedins works with T3, T4, & GH
Heart pump ANP decrease blood pressure
Blood vessels blood pathway endothelin vasoconstriction
Blood transport gases cytokines immune chemical signals
Renal water / pH regulation calcitrol Ca++ reabsorption
Rennin blood pressure
EPO RBC production
Placenta fetal exchange Progesterone maintain pregnant uterine lining
Hypo- below hyper- above, excessive
Acr/o- extremity horm- impulse
Insul- island myx- mucus
-crine secrete thyr/o- thyroid
adren/o- adrenal aden/o- gland
gluc/o- , glyc/o- sugar pituitar/o- pituitary
natri- sodium kali- potassium
calci- calcium iod/o- iodine
-physis growth -emia blood
mega- big -tropin stimulate
Endocrine glands
Make a chart or table that has the major endocrine hormones, target organ, and effects for the following classical endocrine organs/tissues:
Explain how the endocrine system controls the following body systems/organs:
Explain blood work results in reference to the hormone levels
Glucose: blood value is reported to be at 65 mg / dL
Thyroid : blood value is reported to be at 18 micrograms / dL
Cortisol: blood value is reported to be at 52 micrograms / dL
ACTH: blood value is reported to be 95 pg/ml
TSH: blood value is reported to be 8.3 mU/l
Calcium: blood value is reported to be 6.8 mg/dl
Concept Map: Make a concept map of the endocrine system (gross, histo) anatomy, hormones (physiology), targets, and effects based on the table you created in the earlier activity. Include this map in your LAR lab report (if selected) as a document insert or as an additional document PDF scan.
Seasonal affective disorder (SAD) Gigantism
Dwarfism Acromegaly
Diabetes Insipidus Diabetes Mellitus: Type I and Type II
Hyperthyroid,
Pseudohyperparathyroidism
Hyperadrenocortism, Cushing’s Disease
Hypoaldosteronism Addison’s Disease
Goiter Myxedema
Hyperinsulinemia Hypoinsulinemia
Hypoglycemia Hyperglycemia
Hypercalcemia Hypocalcemia
Hyperkalemia Hypokalemia
Hypernatremia Hyponatremia
Hyperpituitarism Hypopituitarism
Endocrinologist
http://www.innerbody.com/htm/body.html
http://www.uvm.edu/~mvalverd/body_endocrine_sys.html
http://www.nku.edu/~dempseyd/THE_ENDOCRINE.htm
http://www.ahealthyme.com/topic/endocrine;$sessionid$OGW1WFQAAABYHWCYSYTDEMQ?_requestid=1562
http://www.nlm.nih.gov/medlineplus/healthtopics.html
http://www.lumen.luc.edu/lumen/meded/histo/frames/histo_frames.html
http://calloso.med.mun.ca/%7Etscott/second.htm
http://www.track0.com/canteach/links/linkbodysystems.html
http://www.carr.lib.md.us/schs/science/anatomy/systems.html
http://www.kcmetro.cc.mo.us/maplewoods/Biology/Bio110/Labs.htm
http://www.stemnet.nf.ca/CITE/body.htm
http://www.medem.com/MedLB/article_detaillb.cfm?article_ID=ZZZW5TZ46JC&sub_cat=514
http://www.nlm.nih.gov/medlineplus/endocrinesystemhormones.html
1. Define hormone
2. Name the chemical classes of hormones and an example of each.
3. Name the hormones of the AP and IP and their function
4. Name the hormones of the PP and their function
5. Name the hormones of the thyroid and their function
6. Name the hormones of the parathyroid and their function.
7. Name the hormones of the adrenal gland and their function
8. Name the hormones of the pancreas and their function.
9. Name the hormones of the gonads and their function.
10. Name the hormones of the kidneys and their function.
11. Name a hormone from a GI system organ and its function
12. Name a hormone from the cardiovascular system and its function.
