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Homeostasis and Endocrine Signaling
Nidhi Ahir, Crystal Tingle, Jennie Bravo
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Introduction● The endocrine system is made up of endocrine glands that
release hormones into the blood● All cells, except for red blood cells, produce
hormonelike substances called prostaglandins○ prostaglandins are modified fatty acids that usually affect only
nearby cells and tissues
● Steroid Hormones are produced from cholesterol. They can cross cell membranes of target cells, bind with the receptors, and change the expression of genes
● this often results in dramatic changes in the cell’s activity
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Introduction Cont.● Nonsteroid Hormones can be proteins, small peptides, or
modified amino acids● they cannot cross cell membranes
○ the receptors are on the cell membrane
● compounds called secondary messengers carry the messages of nonsteroid hormones inside target cells
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the endocrine systemA collection of glands that produce hormones that
regulate metabolism, growth and development, tissue function, sexual function, reproduction, sleep, mood, and many other bodily processes.
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Overview● Anatomy: the study of the biological form of an organism
● Physiology: study of the biological functions an organism performs
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hierarchical organization of animal bodiesCells are organized into:
● Tissues: groups of cells with similar appearance and common function
● Organs: different types of tissues organized into functional units
● Organ Systems: groups of organs that work together
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Complex organ systems of animals● They are built from a limited set of cell and tissues
types
● Tissue types can be grouped into 4 categories: ○ epithelial○ connective tissue○ muscle○ nervous
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Regulating and conforming● Animals are faced with environmental fluctuations, they
manage their internal environment by either regulating or conforming. (interstitial fluid)
● Regulating: uses internal mechanisms to control internal change despite external fluctuation
● Conforming: allows it internal condition to change in accordance with external changes
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Homeostasis● An organism uses homeostasis to maintain a steady state
or internal balance regardless to the external environment
● Animals achieve homeostasis by maintaining a variable at or near a particular value = set point
● Fluctuations above or below the set point = stimulus● These are detected by a sensor and trigger a response● The response returns the variable to the set point
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Homeostasis● In animals, it relies largely on a control mechanism that
reduces the stimulus = negative feedback● Homeostasis moderates, but does not eliminate changes in
the internal environment● Thermoregulation: process by which animals maintain an
internal temperature within a tolerable range.
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Endothermy and Ectothermy● Endothermic: animals generate heat by metabolism, birds
and animals are an example of this
● Ectothermic: animals gain heat from outside sources, most invertebrates like fish, amphibians and nonavian reptiles are examples of this
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Endothermy and Ectothermy● Endotherms can maintain a stable body temperature in
large fluctuations in environmental temperature
● Ectotherms regulate temperature by behavioral means● Ectotherms usually need to consume less food than
endotherms, but the heat source is largely environmental
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Balancing heat loss and gain● Organisms exchange heat by 4 physical processes:
○ radiation○ evaporation○ convection○ conduction
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Circulatory adaptations for thermoregulation● Animals can alter blood (heat) flow between their body
core and skin
● Vasodilation: the widening of the diameter of superficial blood vessels, promotes heat loss
● Vasoconstriction: the narrowing of the diameter of superficial blood, reducing heat loss
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Circulatory adaptations for thermoregulation● The arrangement of blood vessels in many marine mammals
and birds allows for countercurrent exchange
● Countercurrent heat exchangers transfer heat between fluids flowing in opposite directions and reduce heat loss
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Physiological thermostats and fever● Thermoregulation in mammals is controlled by a region of
the brain called the hypothalamus.
● Hypothalamus triggers heat loss/ heat generating mechanisms
● Fever is the result of a change to the set point for the biological thermostat
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2 major systems for controlling & coordinating● Endocrine System
○ signalling molecules (hormones) released into the bloodstream by endocrine cells that reach all locations in the body.
● Nervous System○ neurons transmit signals along dedicated routes, connecting specific
locations in the body
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simple endocrine pathways● Digestive juices in the stomach are extremely acidic and
must be neutralized.● The release of acidic stomach contents into the duodenum
stimulates endocrine cells to secrete the hormone secretin.
● This causes target cells in the pancreas to raise pH in duodenum.○ pancreas can act as an exocrine gland that secretes substances or and
endocrine gland that secreted hormones directly into interstitial fluid.
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Neuroendocrine Pathways● Hormone pathways that respond to stimuli from the
external environment rely on a sensor in the nervous system
● The hypothalamus combine endocrine and nervous systems in vertebrates
● Signals from the hypothalamus travel to the pituitary gland located at its base
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● Signals from the hypothalamus trigger composition and release of hormones from the anterior pituitary
● the posterior pituitary is an extension of the hypothalamus and produces oxytocin○ oxytocin regulates the release of milk during nursing in mammals
● the posterior pituitary also produces ADH (antidiuretic hormone)
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Feedback Regulation in Endocrine Pathways● a feedback loop links the response back to the original
stimulus in an endocrine pathway● while negative feedback dampens a stimulus, positive
feedback supports a stimulus to increase the response
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Pathways of Water-Soluble and Lipid-Soluble Hormones● the hormones previously discussed so far are proteins
that bind to cell-surface receptors and that trigger events that lead to a cellular response
● the intracellular response is called signal transduction● a signal transduction pathway has multiple steps● lipid-soluble hormones have receptors inside cells● when attached by the hormone, the hormone-receptor
complex moves into the nucleus
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Effects of Hormones● many hormones draw out more than one type of response● for example,epinephrine is produced by the adrenal glands
and can raise blood glucose levels, increase blood flow to muscles, and decrease blood flow to the digestive system
● target cells vary in their response to a hormone because they differ in their receptor types or in the molecules that produce the response
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Evolution of Hormone Function● over the course of evolution, the function of a given
hormone may be different between species● For example, thyroid hormone plays a role in metabolism
across many lineages, but in frogs it has taken on a unique function○ in frogs, the thyroid hormone stimulates the resorption of the
tadpole tail during metamorphosis
● Prolactin (hormone used to stimulate milk) also has a broad range of activities in vertebrates
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Osmosis and Osmolarity● Osmoregulation is the term for the processes by which
animals control solute concentrations in the interstitial fluid and balance water gain and loss
● cells need a balance between uptake AND loss of water● Osmolarity is the solute concentration of a solution
○ it determines the movement of water across a selectively permeable membrane
● if two solutions are isoosmotic (have the same osmotic pressure), the net flow of water is from the hypoosmotic to hyperosmotic solution
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Osmoregulatory Challenges and Mechanisms● osmoconformers: consisting of some marine animals, are
isoosmotic with their surroundings and do not regulate their osmolarity
● osmoregulators: expend energy to control water uptake and loss in a hyperosmotic or hypoosmotic environment
● Marine and freshwater organisms have opposite challenges● Marine fish drink large amounts of seawater to balance
water loss and separate and get rid of salt through their gills and kidneys
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Marine Fish● Marine fish drink large amounts of seawater to balance
water loss and separate and get rid of salt through their gills and kidneys
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Freshwater Fish● Freshwater fish drink almost no water and replenish salts
through eating● some also replenish salts by uptake across the gills
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● land animals have mechanisms to prevent dehydration such as:○ body coverings that help reduce water loss○ drinking water○ eating moist foods○ producing water metabolically
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Nitrogenous Wastes● the type and quantity of an animal’s waste products may
greatly affect its water balance● among the most significant wastes are nitrogenous
breakdown products of proteins and nucleic acids● some animals convert toxic ammonia (NH3) to less toxic
compounds prior to excretion
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● ammonia excretion is most common in aquatic organisms● vertebrates excrete urea
○ a conversion product of ammonia, which is much less toxic
● insects, land snails, and many reptiles (including birds) excrete uric acid as a semisolid paste (BIRD POO POO)
● it is less toxic than ammonia and generates very little water loss○ but it is energetically more expensive to produce than urea
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Excretory Processes● in most animals, osmoregulation and metabolic waste
disposal rely on transport epithelia○ a membrane transporter that transports substances across the
epithelium
● these layers of epithelial cells are specialized for moving solutes in controlled amounts in specific directions
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● many animal species produce urine by removing a filtrate derived from body fluids
● key functions of the most excretory systems○ filtration: filtering of body fluids○ reabsorption: reclaiming valuable solutes
○ secretion: adding nonessential solutes and wastes from the body fluids to the filtrate
○ excretion: releasing processed filtrate containing nitrogenous wastes from the body
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Invertebrates● No backbone ● Protonephridia-Excretory system of Flatworms● Flame Bulb-Smallest branches of network
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Vertebrates● Has a backbone● Animals have highly developed brain● Kidney functions in both osmoregulation and excretion● Excretory System includes ducts ● Humans are vertebrates● Fish, Primates, Reptiles, Birds
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Bowman's Capsule● Capillaries and specialized cells ● Permeable to water and small solutes ● Produces a filtrate
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Proximal Tubule ● Reabsorption ● Molecules are transported● Toxic materials secreted into filtrate
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Descending limb of loop of henle● Reabsorption continues through channels, formed by
aquaporin proteins ● Movement driven by high osmolarity of interstitial fluid● Filtrate becomes concentrated ● First part of the loop of Henle
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Ascending limb of loop of henle● Transport epithelium ● Salt but not water move from tubule into interstitial
fluid● Filtrate becomes dilute
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Distal tubule● Regulates the K+ and NaCl and reabsorbs ● Controlled movement of ions Contributes to pH Regulation ● Main function is Secretion ● Most distal portion of Nephron ● forms part of the juxtaglomerular apparatus● Juxtaglomerular apparatus controls of systemic blood
pressure and volume
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Collecting Duct ● Carries filtrate through medulla to the renal pelvis ● Reabsorbed into blood● Urine is hyperosmotic to body fluids● participates in electrolyte and fluid balance ● network of small tubes that act as a drainage system in
the body● Here it is where large amount of urine is produced (what
you feel when you can't hold it)
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Concentrating urine in mammalian kidney ● An important adaptation to life on land● Its functional unit is the nephron● Each nephron consists of a glomerulus, situated in the
cortex of the kidney● Consists of an outer cortex and inner medulla
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Adaptations of vertebrate kidney to diverse environments● Animals Kidneys adapt differently● Dessert mammals have long loops of Henle● Birds have short loops of Henle ● Mammals control volume and osmolarity of urine● The South American bat can produce dilute or concentrated
urine
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Homeostatic Regulation of Kidney ● The kidney is one of your most important organs of
homeostasis ● A combination of nervous and hormonal inputs ● Inputs contribute to homeostasis for blood pressure and
volume● Keeps fluid balanced● filters fluids and wastes through the body
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Antidiuretic Hormone● ADH● An increase in blood osmolarity above a set point
triggers the release of ADH ● Decreased osmolarity causes a drop in ADH secretion ● can treat diabetes insipidus● can increase blood pressure in patients with vasodilatory
shock
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Renin-Angiotensin-Aldosterone System ● RAAS Regulates kidney function● Regulates blood ● determinant of target-organ damage● The juxtaglomerular apparatus (JGA) releases enzyme renin● Triggers formation of peptide Angiotensin II
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Angiotensin 2 ● peptide hormone● involved in the process of repair and vascular/ muscle
damage ● Raises blood pressure● important part of neurohumoral activation in heart
failure● Stimulates release of the hormone aldosterone
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Similarities & differences between ADH & RAAS● Both increase water reabsorption ● ADH responds to changes in blood osmolarity ● RAAS responds to changes in blood volume & pressure● Both work together to keep homeostasis going in our body
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