Biology Chapter 45: Hormones and the Endocrine System

Hormones and the Endocrine System

• Hormones are chemical signals secreted into the circulatory system, conveying regulatory messages throughout the body.
• Hormones affect target cells with specific receptors.
• Metabolism and development hormones, while reaching all parts of the body, affect only target cells possessing receptors specific to those hormones.

Communication and Regulation Systems

• Chemical signaling via hormones is a function of the endocrine system which regulates reproduction, development, energy metabolism, growth and behavior.
• The nervous system, a network of specialized cells (neurons), transmits signals along dedicated pathways, regulating neurons, muscle, and endocrine cells.
• The nervous and endocrine systems often work together and neuronal signaling can regulate hormone release.

Intercellular Information Flow

• Animal cell communication via secreted signals can be classified according to:
  • The type of secreting cell
  • The route of the signal to its target

Paracrine and Autocrine Signaling

• Local regulators are molecules acting over short distances and reaching target cells via diffusion
• Paracrine signaling affects the target cells lying near secreting cells
• Autocrine signaling, the target cell is also the secreting cell.
• Processes such as blood the pressure regulation, nervous system function, adaptive immunity, and reproduction employ paracrine and autocrine signaling.

Classes of Local Regulators

• Local regulators act on their target cells in seconds/milliseconds.
• They are typically polypeptides, including:
• Cytokines for immune responses
• Growth factors for proliferation and differentiation
  • Granulocyte-macrophage colony stimulating factor
  • Platelet-derived growth factor
  • Epidermal growth factor and nerve growth factor
• Prostaglandins can be modified fatty acids which function in the immune system and blood clotting.
• Gases can be local regulators
• Nitric oxide (NO) serves as a neurotransmitter and local regulator

Immune Cell Communication

• Immune cells communicate with each other utilizing cytokines as local regulators.
• The target cells lie near the secreting cells in paracrine signaling
• The target cell is the secreting cell in autocrine signaling.

Prostaglandins (PGs) Functions

• They have reproductive, immune system and/or blood clotting functions in the body
• Male prostate glands secrete PGs into semen, which results in uterine wall contraction to help sperm reach the egg.
• Female placenta secretes PGs that helps induce uterine contractions during childbirth, making uterine muscles more excitable.
• They promote fever, inflammation, and intensify pain in the immune system (macrophages enhancing body defense).
• Aspirin and ibuprofen's anti-inflammatory effects is due to PG synthesis inhibition.
• They regulate platelet aggregation in blood clot formation to reduce heart attack risk with low aspirin doses.
• They are necessary to maintain the stomach's protective lining, however, long term aspirin therapy can cause stomach irritation.

Nitric Oxide (NO) Activity

• Endothelial cells synthesize and release NO when blood oxygen is too low.
• The NO activates surrounding smooth muscle cell relaxation which improves blood flow by dilating the blood vessel walls.
• NO is important in male arousal, increasing blood flow to the penis, causing an erection.
• Viagra sustains erections by prolonging NO pathway activity.

Synaptic and Neuroendocrine Signaling

• In synaptic signaling, neurons create specialized junctions (Synapses) with target cells (other neurons and muscle cells).
• Secreted neurotransmitters (Acetylcholine) diffuse across synapses to bind receptors on target cells in Synaptic Signaling.
• The specialized neurosecretory cells of neuroendocrine signaling secrete neurohormones that then diffuse from nerve endings into the bloodstream.
• Antidiuretic hormone (ADH) / Vasopressin is a neurohormone critical in water balance and kidney function.

Endocrine Signaling

• Hormones secreted by endocrine cells travel through extracellular fluids via the bloodstream to reach their targets.
• This signaling maintains homeostasis, regulates growth and development, and mediate response to stimuli
• Stress and dehydration is coordinated, as well as controlling low blood glucose.

Chemical Classes of Hormone Regulators

• Hormones can be classified into three major chemical classes
• Amines
• Polypeptides
• Steroids
• Molecules used in intercellular signaling vary in size and chemical properties.

Classes of Hormones

• Hormones classify into three major classes
• Polypeptides like Insulin, which has 2 polypeptide chains made via longer protein chain cleavage.
• Amines such as epinephrine, oxytocin, and thyroxine, are synthesized from single amino acids, either tyrosine or tryptophan.
• Steroids like cortisol and ecdysteroid, are lipids with four fused carbon rings.
• Polypeptides and amine hormones are water-soluble.
• Steroid hormones and other nonpolar hormones are generally lipid-soluble.

Cellular Response Pathways

• Water-soluble hormones secreted by exocytosis travel freely in bloodstream, but only binding to cell-surface receptors.
• It induces changes in cytoplasmic molecules.
• Upon receptor binding, it initiates signal transduction pathways, which then leads to response in enzyme activation, cytoskeleton response, or gene expression change.
• Lipid-soluble hormones diffuse across cell membranes, travel in the bloodstream using transport proteins, and then diffuse through the target cell membrane
• Binding to intrareceptors triggers gene transcription changes in the nucleus/cytoplasm.

Water-Soluble Hormone Pathway (Signal Transduction)

• The signal transduction pathway converts extracellular chemical signal to a specific intracellular response
• The hormone epinephrine secreted by the adrenal mediates the body's responses to short-term stress.
• Epinephrine binds to G-protein-linked receptors on liver cell plasma membranes.
• It triggers the second messenger cyclic AMP (cAMP) synthesis when binds.
• The cAMP activates protein kinase A, that then activates an enzyme for glycogen breakdown, while simultaneously inactivating an enzyme for glycogen synthesis.
• This results in the liver releasing glucose into the bloodstream, providing the needed fuel to address a stressful situation

Lipid-Soluble Hormone Pathway

• Intracellular receptors perform the entire signal transuding task within a given target cell for lipid-soluble hormones.
• Steroid hormones bind to a cytosolic receptor
• A receptor complex forms, moves into the nucleus, and induces a gene expression change.
• The receptor part then acts as a transcriptional specific target genes regulator and interacts with a specific DNA-binding protein.
• Estradiol, a form of estrogen, binds to a cytoplasmic receptor in liver cells of female birds and frogs.
• The receptor that is estradiol bound triggers transcription for egg yolk production vitellogenin genes.

Hormone Variability in Lipid Soluble Pathways

• Thyroxine, vitamin D, and other nonsteroid lipid-soluble hormones usually have receptors in the nucleus.
• Hormone molecules diffuse through the plasma membrane and the nuclear envelope prior to transcription stimulus at specific DNA receptor sites.

Multiple Hormone Effects

• Same hormones may have different effects on target cells that have different receptors for the hormone
• The target cells can have different signal transduction pathways leading to different outcomes.

Endocrine Hormone Secretion from Tissues and Organs

• Some endocrine cells are in organs and tissues, that are part of other organ systems.
• An example is the stomach secreting gastrin.
• Other endocrine cells group together, creating endocrine glands in the ductless organs.
• Endocrine glands secrete hormones directly into the surrounding fluid for diffusion into the circulatory system.
• Exocrine glands (salivary glands) secretes substances onto the body surface through ducts

Mammalian Endocrine Glands

• Pineal Gland secretes Melatonin which participates in regulation of biological rhythms.
• Hypothalamus:
• Hormones are released from the posterior pituitary (oxytocin and vasopressin)
• Releasing and inhibiting hormones regulate the anterior pituitary
• Anterior Pituitary:
• Follicle-stimulating hormone (FSH) and luteinizing hormone (LH): stimulate ovaries and testes
• Thyroid-stimulating hormone (TSH): stimulates thyroid gland
• Adrenocorticotropic hormone (ACTH): stimulates adrenal cortex
• Prolactin: stimulates mammary gland cells
• Growth hormone (GH): stimulates growth and metabolic functions
• Posterior Pituitary:
• Oxytocin: stimulates contraction of smooth muscle cells in uterus and mammary glands
• Vasopressin, also called antidiuretic hormone, ADH): promotes retention of water by kidneys; influences social behavior and bonding
• Thyroid Gland:
• Triiodothyronine (T3) and Thyroxine (T4): Stimulates and maintains metabolic processes
• Calcitonin: Lowers blood calcium level
• Parathyroid Glands:
• Parathyroid hormone (PTH): Raises blood calcium level
• Adrenal Medulla secretes epinephrine and norepinephrine:
• Raises blood glucose level
• Increases metabolic activities
• Constricts certain blood vessels
• Adrenal Cortex secretes:
• Glucocorticoids: Raises blood glucose level
• Mineralocorticoids: Promotes reabsorption of Na+ and excretion of K+ in kidneys
• Pancreas secretes:
• Insulin: Lowers blood glucose level
• Glucagon: Raises blood glucose level
• Ovaries (female) secrete:
• Estrogens: stimulate uterine lining growth and promote development and maintenance of female secondary sex characteristics
• Progestins: Promote uterine lining growth
• Testes (male) secrete:
• Androgens: Support sperm formation, promote development and maintenance of male secondary sex characteristics
• Hormone can be found in both males and females

Feedback Regulation and Coordination

• Hormones are combined into regulatory pathways
• Simple pathways respond to a stimulus by secreting a particular hormone by the endocrine cells.
• Neuroendocrine pathways are controlled by the nervous system.
• Hormones can be
• Nontropic: Hormones direct effect on cells
• Tropic: Hormones act on other endocrine glands

Neuroendocrine and Simple Pathways

• A simple neuroendocrine pathway stimulus is sensed by a sensory neuron, which then stimulates a neurosecretory cell.
• Neurosecretory cells then secrete a neurohormone, entering the bloodstream and travels to target cells.
• Constant internal conditions are maintained with homeostasis, and feedback regulation connects response to the stimulus in control pathways.

Feedback Regulation Specifics

• The Negative feedback loop reduces initial stimulus response, preventing excessive pathway activity and restoring homeostasis.
• This helps maintain Calcium levels in the blood and blood sugar.
• Positive feedback amplifies both stimulus and response
• Oxytocin causes milk release via suckling offspring to release more oxytocin in mammals.
• Muscle contraction occurs in birth when oxytocin induces target cells within uterine muscles.

The Homeostatic Systems

• Homeostasis restore a pre-existing state, and metabolic balance depends on maintaining blood/glucose concentrations near about 90 mg/100 ml.
• Sets of simple hormone pathways with coordinated activities
• Paired pathways with stimulation and inhibit

The Blood Sugar Controls

• When glucose concentration exceeds the set point, insulin triggers glucose uptake, lowering the blood glucose.
• When blood glucose falls below set point, that release of glucose from liver happens from liver glycogen, increasing blood glucose.
• Both antagonistic glucagon and insulin regulate blood glucose levels, and are regulated by negative feedback within a simple endocrine pathway.

Endocrine Gland

• Endocrine System:
  • Communicators are are chemical hormones transmitted in the blood.
  • The response is slower and more prolonged
• Nervous System:
  • Nerve impulses for communication

Butterfly Lifecycle

• The endocrine pathway controlling larval molting starts in larval brain neurosecretory cells, producing prothoracicotropic hormone (PTTH), which is a neurohormone polypeptide.
• The PTTH direct release of ecdysteroid.
• Bursts of ecdysteroid is what triggers each successive molt as well as metamorphosis.
• Juvenile hormone (JH) controls ecdysteroid activity timing.
• Metamorphosis occurs when JH levels drop.

Vertebrate Control Systems

• Link the nervous system to anterior/posterior pituitary gland (Hypophysis).
• Hypothalamus receive information from nerves throughout the body and then initiates the necessary neuroendocrine signals.
• The hypothalamus then coordinates pituitary activity to assist with body temp, thirst and to control other homeostatic factors.
• The hypothalamus' signals are relayed to both anterior / posterior pituitary gland

Pituitary Hormones

• The posterior pituitary gland preserves and releases the hypothalamus-made hormone from its extension.
• The anterior pituitary synthesizes/releases the hormone under hypothalamic control, creating endocrine gland.

Posterior Pituitary Hormones

• The hypothalamus neurosecretory cells synthesize the posterior pituitary hormones.
• Antidiuretic hormone (ADH), or vasopressin, is released from the posterior in response to higher blood concentration.
  • The kidneys then increases retention that lowers the urine volume.
• Negative feedback, allows blood concentration to be normal with reabsorption, ADH shuts off.
• It also influence social behavior.
• Oxtocin- neurological impulses create uterine secretions that stimulates contractions for milk production and births..

Anterior Pituitary Hormones

• The anterior pituitary has control of diverse processes, as metabolism, osmoregulation, and reproduction.
• All anterior pituitary hormone production is under control of releasing / inhibiting hormones secreted through the hypothalamus.
• This allows them to release/secrete milk.
• Capillaries near the hypothalamus release the hormones and allow portal vessels to be secreted.
• The blood then feeds into the capilary of the anterior pituitary.
• The releasing hormone then goes to the gland it controls.

Hormones Cascade Pathways

• Hypothalamus hormones, anterior pituitary hormones, and target endocrine glands are often formed through hormone cascade pathways.
• These pathways creates tropic hormones acting in a chain reaction.
• Tropic hormones then stimulate the beginning of other endocrine glands to release non-tropic.
• Nontropic hormones then take on any other endocrine glands by end of the chain reaction.

Thyroid Axis of Pituitary

• Three pituitary hormones create a target effect that then has a glands effect
• Thyroid/Stimulating Hormone- then creates thyroid hormones
• ACTH stimulates cortex to then produce glucocorticoids
• Gonadotropic Hormone (LH and FSH) then has an effect on ovaries to create testosterone

Control Mechanisms in Mammals

• The body controls thyroid hormone levels using cascade pathway.
• Humans, when having thyroid hormone then have metabolic processes
• if it drops, the hypothalamus releases TRH,
• TRH will then cause an increase of TSH from anterior,
• Then the TSH stimulates thyroid gland that releases a somatostatin inhibiting pituitary and gland.
• Negative feedbacks have occurred through original stimulus/ target cells with hormone.

Thyroid Disorders

• Not enough production that lead to issues
• Hypothyroidism- is where hormone is not produced and needs to have extra hormone to activate
• Hashimoto- where Abs destroy the thyroid.
• Overproduction of active thyroid and symptoms- have symptoms like weight issues, high Bs, and irritation
• Graves disease- hyperthyroidism cause nervous activity heart.
• A goiter from pituitary occurs if pituitary keeps secreting glands.
• Cretinism- untreated and short individual with poor lifestyle of issues.
• Malnutrition- I in body as only in thyroid.
• Has two hormes which helps synthesize iodine (T and T)

Hormones and Growth

• Growth hormone stimulate the anterior pituitary, and have both tropic actions on liver and cartilage.
• Tropic action allows signal to liver/ release IGF- (Insulin Like Growth Factors)
• Deficiency/ Excess of (GH)- in excess- cause giantism while a lack causes (D)- drawfishm.
• GH exerts metabolic effects, raising blood gluc levels and inhibiting insulin. Somatostatin IN (inhinits glands to secretion)

GH Hormones

• Genetic issues can have an affect at the body having growth issues.
• Excessive- Gigantism is the excessive of production GH while low production affects ( Dwarfism)

Steroid Horomes in Body

• Not growing or in the bone issues. -Acromegaly- (hands feet will be large) bone in face
  • There are also tropic hormonal functions.

Non-tropic Hormones

• Hormones that act-and bind to tissues to cause production, the MSH, then binds to melanin to produce.
  • Prolactin can then be used for women- helps with lactation then synthesize the milk
  • Metabolism fat in body are synthesized .

Control by the Feedback of Hormones

• A disruption of levels in the body causes- a domino effect for the system
• Feedback affects the effects of these- in the body

Parathyroid Hormone

• Constant regulation- the muscles and skeletal are controlled
• the function is due to cells in the body due to Ca- and this then leads too tetany for falling.
  • The calcium cannot react

Calcitonin Control

• Calcium has too get to body/ it creates a precipitatum
  • Metastatic Ca causes it to build to tissues and kidney.
• Two Hormones for Homoestasis:
  • the igenousness of mammals/ calcium level
  • the gland release is for all types.

Parathyroid Gowns

• Parathyroid Glands and tissue cause gland to help and blood Ca.
• Is normally 10 Mg in the body
• PTH help increase body tissue
• Effect bones Kidneys:
  • Has a matrix from the kidney for bone tissue, has oestoraclsts to then let of back and forth in the body
• Kidneys- then reabsorphs tissue for tubes and what the body needs it

Ca Hormones

• Kidneys Stimulates the- Vitamin D in the Liver to support/ supplement.
• The skin creates D in sun
• Liver is from the kidney to help get tissue.
• Vitamin 4- active forms and is in intersine tissue.

The Bone

• Bone- brittle density that causes bones to fall
• Osteoproses, the absorpbs, and has tissue.
• Hormone Changes- the mineral help the (PTH)- the D vitamin that helps
• Treatment- helps with bisphosphonates

Ca Levels and Release

• Negative Feedback- from glands due level in body it is a loop back and forth with what hormones need
• CAL is for - (Calcium Control).
• the calcium is for oestrbalsy that comes by
• Tissue and has then gets in to help increase body

Suprarenal Glands

• Has the adrenic glands over the area to protect the tissue
• Adrenal glands consist of Medusa and tissue itself
• Neuroendocrine to tissue:
  • has medusa that has all cells that help with tissue that goes away
• Cortex adrenal are endocrine cells itself.

Adrenal Medusa Medulla-

• Tissue and the adrenaline help release this and tyrosine and neurotransmitters.
• This will lead to flight/flight- signals of reactions.
• Involuntary new receptors help affect.

Tissue Functions

• Epinephrine- to help for glycogen in the body
• Break tissue to help
• Muscles Liver- Brain help support muscle/ tissue to the brain, and digestive organs for Kidneys
• Heart- increased rate- and stroke, and increases in a dilated way.

Streoid Hormones

• They respond with cortex to- the level pressure
• Reacts and then stimmulates to release hormone (ACTH)- to A cortex.
• The steroids to stress is helped.
• ACT H- has tissue help/ then steroid creation release and this the is
• Corticosteroid .

Corticoid

• Has to control
• Glucose
• Has- Salt and mineral levels
• Has - Kidney for renin (horm) to not have Pituitary.

Body Health help

• Gluecotcoids has help- that help use body
• Then amino are transported.

Vasolidation-

• (ANP)- Atrial peptides- Tissue controls
• Help help- body with pressure- and has dilators- in blood.

Endocrine Problems

• Has gland disorder:
• Disruption - can then result with problems like- Addison’s disease to Abs.
• The destruction then the symptoms causes the lack effect is the Mineral issues.

Anterior Problems

• The An then has to gonad- then gonadotrophins- this means and hormones from L ( hormone release) to LH.
• Ovaries help- to the hormone release- Estrogen- hormones are then- adrenaline of the hormone.
• The sex hormone are in the women.

Body functions with it-

• For sex issues-
• Affects Development - Affects sex in areas/ for the behavior.
• Androgen is responsible- testosterone in the man.
• Oversee the main issues/ and to body of care

Estrogen Hormone

• Controls body from all areas the estrogen help with these in women.
• DHT(dihydrotestosterone)- the hormone that creates the problems.

Hormones Issues

• Between 1938 to 71 to have complications
• Some- were estrogenic by DES / caner

Tissue Help For This-

• SCN helps, and releases.
• That hypothalamus area.
• Then it will regulate the help from these.
• SCN comes out and that that point causes that

Tissue Issues

• In frog/ human the control by the function, the tyraxioien controls
• Reserptiion function are.
• Mammals- pro action, and the stimulation.
• Then tissue is related- and the water balance issues.
• MSH help/ regulates- then helps, and to function,