Exam 1: Sense Organs, Endocrine, and Reproductive Systems PDF

# Exam 1: Sense organs, endocrine, and reproductive systems ## What is sensation? What is perception? - **Sensation:** Physical process (intensity). Sensory information gets sent to the thalamus, then the prefrontal cortex in order to relay information. An example includes touching hot water to se...

# Exam 1: Sense organs, endocrine, and reproductive systems ## What is sensation? What is perception? - **Sensation:** Physical process (intensity). Sensory information gets sent to the thalamus, then the prefrontal cortex in order to relay information. An example includes touching hot water to see how hot it is and then reflexively pulling your hand back due to the intensity of the heat - **Perception:** The processing of sensory information to make sense of its significance. - It involves both physiological and mental processing, enabling conscious awareness of the environment. - Attention determines what stimuli continue to the level of perception after being sensed. - Example: Smell gets sent to the primary olfactory cortex. Smells like methanol are very intense and cause nasal cavities to burn and eyes to water, which causes people to perceive that the smell is not safe to ingest or really inhale. ## What is transduction and absolute threshold? - **Transduction:** The conversion of one form of energy to another. - The fundamental purpose of any sensory receptor is conversion of stimulus energy (like light, heat, touch, and sound) into nerve signals. - **Absolute threshold:** The minimum stimulus that causes a change in signal transduction. ## What is modality and labeled line code? - **Modality:** The type of stimulus or sensation it produces (like vision, hearing, and taste). - **Labeled line code:** All action potentials are identical; each nerve pathway from sensory cells to the brain is labeled to identify its origin. The brain uses these labels to interpret what modality the signal represents. - Example: An action potential for vision is identical to an action potential for taste—smelling a dead deer can cause you to taste the dead deer. ## What is the difference between intensity and duration? - **Intensity**: The brain distinguishes stimuli intensity by: 1. Which fibers are sending signals 2. How many fibers are doing something 3. How fast these fibers are firing - **Duration**: How long the stimulus lasts. Changes in firing frequency occur over time. Sensory adaptation: If a stimulus is prolonged, firing of the neuron gets slower over time (like adapting to hot bathwater). ### What is an example of tonic and phasic receptors? - **Tonic receptors**: Adapt slowly and generate nerve signals more steadily throughout the presence of the stimulus. - Example: **Proprioceptors**: Body position, muscle tension, and joint motion. - **Phasic receptors**: Adapt rapidly and generate a burst of action potentials when first stimulated, then quickly reduce or stop signaling even though the stimulus continues. - Example: Smell, hair movement, and cutaneous pressure. ## What are the different encapsulated and unencapsulated nerve endings? - **Encapsulated nerve endings**: Wrapped by glial cells or connective tissue, which enhances sensitivity or selectivity of response. - **Tactile (Meissner) corpuscles:** Light touch and texture (example: Dermal papillae of hairless skin like fingertips, eyelids, and palms). - **Krause end bulbs**- tactile; located in mucous membranes in lips and tongues and is responsible for the mouth being so sensitive - **Lamellar (Pacinian) corpuscles:** Deep pressure, stretch, tickle, and vibration (found in dermis). Periosteum of bone, and deep dermis of skin - **Bulbous (Ruffini) corpuscles:** Heavy, touch, pressure, and joint movements. - **Unencapsulated nerve endings**: Lack connective tissue wrappings. - **Tactile (Merkel) discs:** Light touch and texture (found in the epidermis basal layer). Example—light touch from a bug on your skin. - **Hair receptors:** Coil around a hair follicle. Monitor movement of hair, adapt quickly. - **Free nerve endings:** Pain and temperature (skin and mucous membranes). Example: Feeling a paper cut. ## Which ones are phasic and tonic? - **Phasic**: Lamellar (Pacinian) corpuscles, tactile (Meissner) corpuscles. - **Tonic**: Bulbous (Ruffini) corpuscles, free nerve endings, tactile (Merkel) discs. ## What receptors receive pain input? - **Free nerve endings**: Specifically **nociceptors**. - **Fast pain**: Travels myelinated fibers at 12-30ms (sharp, localized, stabbing pain perceived with injury). - **Slow pain**: Travels unmyelinated fibers at 0.5-2ms (longer-lasting, dull, diffuse feeling). - **Somatic pain**: From skin, muscles, and joints. - **Visceral pain**: From viscera (organs). - Stretch, chemical irritants, or ischemia of viscera. - **Bradykinin** is the most potent pain stimulus. - **Histamine, prostaglandin, and serotonin** stimulate nociceptors. # Anatomy of the lingual papillae - **Lingual papillae** are bumps on the tongue where taste buds sit. - **Filiform papillae**: Contains no taste buds and helps sense food texture. - **Foliate papillae**: Weakly developed (taste buds degenerate by age 3). - **Fungiform papillae**: Contain a few taste buds (at the tips and sides of the tongue). - **Vallate or circumvallate papillae:** Located at the rear of the tongue in a “V” and contains up to 1/2 of all taste buds. ## Where on the tongue can you find sweet, salty, bitter, umami, and sour? - **Tip of the tongue**: Sweet - **Edges of tongue**: Salty and sour. - **Rear of tongue**: Bitter. - **Entire tongue**: Umami. ## What types of taste use secondary G-proteins or directly depolarize the membrane? - **Sweet**: (Sugars) binds to receptors to activate G proteins and second-messenger systems within the cell. - **Alkaloids (bitter)**: Binds to receptors to activate G proteins and second-messenger systems within the cell. - **Glutamate (umami)**: Binds to receptors to activate G proteins and second-messenger systems within the cell. - **Salty (sodium)**: Penetrates the cell to depolarize them directly. - **Sour (acids)**: Penetrates the cell to depolarize them directly. ## Which cranial nerves innervate the tongue and for taste? - **Facial nerve (VII):** Collects sensory information from taste buds from over 2/3s of the anterior tongue; sweet tastes. - **Glossopharyngeal nerve (IX):** From the posterior third of the tongue: Salivation and bitter and sour taste. - **Vagus Nerve (X):** From taste buds of the palate, pharynx, and epiglottis: Swallowing, gag reflex, vomiting, and taste from the epiglottis and pharynx (feeling full after eating). # Anatomy of olfaction - **Olfactory mucosa** is a pseudostratified columnar epithelium in the nasal cavity. - **Olfactory cells** are neurons shaped like bowling pins with head bears that have 10-20 cilia called **olfactory hairs**. - **Fascicles** in the olfactory cells are collectively regarded as the **olfactory nerve** (cranial nerve I). The basal end of each cell becomes the axon, the axons collect into small fascicles and leave cranial cavity through the cribriform foramina in the ethmoid bone. ## What bone do the olfactory fascicles travel through? - **Ethmoid bone.** ## How can you get meningitis from picking your nose? - Picking your nose can contribute to the colonization of **Streptococcus pneumoniae** (the bacteria that causes meningitis) in your nose. The bacteria can pass through the nose and into the bloodstream. # Physiology of Smell - **Odorant molecules** bind to **membrane receptors** on olfactory hair. - **Hydrophilic odorants** diffuse through mucus and bind directly to the receptor. - **Hydrophobic odorants** are transported by **odorant-binding proteins** in mucus. - **Odorants** activate **G protein and cAMP system** in olfactory cells, which opens **ion channels** for sodium or calcium, which **depolarizes the membrane** and creates **receptor potential**. This triggers the **action potential** that travels to the brain. - **Odorants** (like ammonia, menthol, chlorine, and capsaicin) can act on nociceptors of the trigeminal nerve. - **Olfactory cells** synapse in the olfactory bulb on dendrites of **mitral and tufted cells**. - **Dendrites** meet in **spherical clusters (glomeruli)**. - **Tufted and mitral cell axons** form the **olfactory tracts** that go to the **primary olfactory cortex** in the inferior surface of the temporal lobe or the **secondary destinations** (hippocampus, amygdala, hypothalamus, insula, and orbitofrontal cortex). ## Why does olfaction not travel through the thalamus? - **Primary olfactory cortex** in the temporal lobe, and the **secondary destinations** (hippocampus, amygdala, hypothalamus, insula, and orbitofrontal cortex) in order to identify odors, integrate with taste, evoke memories, emotions, and visceral reactions. ## What is pitch and loudness? - **Pitch**: Our sense of whether a sound is “high” or “low”. It is determined by **vibration frequency** (Hertz) or cycles/second. - **Infrasonic**: Frequency below 20Hz. - **Ultrasonic**: Frequency above 20,000Hz (Speech is 1,500 to 5,000Hz where hearing is most sensitive). - **Loudness**: The perception of sound energy, intensity, or amplitude of the vibration, expressed in **decibels (dB)**. ## How do these relate to deafness? - Most hearing loss with age is in the range of 250 to 2,050Hz. Prolonged exposure to sounds above 90dB can cause damage or hearing loss. ## What is conductive and sensorineural deafness? - **Conductive**: Conditions interfere with the transmission of vibrations to the inner ear. Examples: - Damaged tympanic membrane - Otitis media - Blockage of the auditory canal - Otosclerosis (fusion of auditory ossicles that prevents their free vibration). - It is **reversible**. - **Sensorineural (nerve)**: Death of hair cells or any nervous system elements concerned with hearing. - Common in factory workers, musicians, and construction workers. - It is **not reversible**. ## How does sound transmit to vibrations in the ear and become action potentials on the vestibulocochlear nerve? - **Outer ear**: Serves as a funnel for conducting vibrations to the **tympanic membrane (eardrum)**. - **Auricle (pinna)** directs sound down the **auditory canal**. - **Auditory canal (external acoustic meatus)** is the passage through the temporal bone to the **tympanic membrane** (contains guard hairs that protect the outer end of the canal and cerumen). - **Middle ear**: Contains the **tympanic membrane**, which closes the inner end of the auditory canal. - **Tympanic membrane**: Innervated by sensory branches of the vagus and trigeminal nerves and is highly sensitive to pain. - The **tympanic membrane** vibrates freely in response to sound. - The **tympanic cavity** contains the **auditory ossicles** (malleus, incus, and stapes—stapes is where the inner ear begins). - **Eustachian tube (auditory tube)** connects the middle ear to the nasopharynx to equalize air pressure on both sides of the ear eardrum. - **Inner ear**: Contains the **bony labyrinth**. ## What is the anatomy and physiology of the inner ear? - The **inner ear** contains the **cochlea**, a structure that has three fluid-filled chambers separated by membranes. - The **spiral organ of Corti** is located within the cochlea and contains **epithelium composed of hair cells and supporting cells**. - **Hair cells** have long, stiff microvilli called **stereocilia** on the apical surface (tectorial membrane rests on top of stereocilia). There are four rows of hair cells spiraling along its length. - **Inner hair cells**: A single row of about 3,500 cells that provides for hearing. - **Outer hair cells**: Three rows of about 20,000 cells that adjust the response of the cochlea to different frequencies and increases precision. ## What are the fluid-filled chambers in the cochlea? - **Scala vestibuli**: (Superior chamber filled with perilymph) - **Scala tympani**: (Inferior chamber filled with perilymph) - **Scala media** (cochlear duct: middle chamber filled with endolymph). - Separated from the scala vestibuli by the **vestibular membrane (Reissner's)** and from the scala tympani by the thicker **basilar membrane**. ### Where is the organ of Corti and what does it do? - **Organ of Corti**: Located in the inner ear (in the cochlea). It converts vibrations into nerve impulses. - **Contains epithelium composed of hair cells and supporting cells**. ### What do the inner and outer hair cells do? - **Inner hair cells**: Provides hearing. - **Outer hair cells**: Adjusts the response of the cochlea to different frequencies and increases precision. ## How is equilibrium maintained? - The **semicircular canals and vestibule** of the inner ear. ### What structures are for dynamic equilibrium? - The **semicircular ducts** detect rotary movements and are held within the semicircular canals. Each duct is filled with endolymph and opens up as a dilated sac (ampulla) next to the macula utricle. Spatial orientation of canals causes ducts to be stimulated by rotation in different planes. ### What structures are for static equilibrium? - The **macula sacculi** (lies vertically on the wall of the saccule) and **macula utriculi** (lies horizontally on the floor of the utricle) are involved (**macula**: 2 by 3mm patch of hair cells and supporting cells in the saccule and utricle). Each hair cell is embedded in a gelatinous otolithic membrane. When head is tilted, heavy otolithic membrane sags, bending the stereocilia and stimulating hair cells. ## What does the semicircular canals do? - **Semicircular canals**: Detect rotary movements. ### What is the crista ampullaris? - Consists of hair cells with stereocilia and a kinocilium buried in a mound of gelatinous membrane called the **cupula** (one in each duct). ## What are the ampullae and what are their functions? - **Ampullae**: Dilated sacs next to the utricle. They contain the crista ampullaris. Their function is to help maintain balance and orient our space. ## What is the macula and what is the function? - The **macula** is a 2-3mm patch of hair cells and supporting cells in the saccule and utricle. Its function is to detect vertical linear acceleration. - **Macula sacculi**: Lies vertically on the wall of the saccule (responds to vertical acceleration and deceleration). - **Macula utriculi**: Lies horizontally on the floor of the utricle. - The **macula** acts as a sensor that detects vertical linear acceleration and deceleration. # Anatomy and Physiology of the Eye - The eye is composed of a series of lenses and spaces that give focus to images. The three principal components of the eyeball include: - **Three layers**: The wall of the eyeball - **Optical components**: that admit and focus light - **Neural component**: Retina and optic nerve. ## What are three tunics of the eye? - **Tunica fibrosa**: The outermost layer, which contains: - **Sclera**: Dense, collagenous white of the eye. - **Cornea**: Transparent region of modified sclera in the front of the eye that transmits light. - **Tunica vasculosa (uvea)**: The middle vascular layer, which consists of: - **Choroid**: Highly vascular, deeply pigmented layer behind the retina - **Ciliary body**: Muscular ring around the lens that supports the lens, iris, and aqueous humor. - **Iris**: Colored diaphragm controlling the size of pupil. - **Tunica interna**: The inner layer, which contains: - **Retina**: Beginning of the optic nerve ### Where are blood vessels found? - **In the choroid**. ## What is emmetropia and accommodation? - **Emmetropia**: The eye relaxed and focused on an object more than 20ft (6m) away. Light rays coming from that object are essentially parallel and rays focused on the retina without effort. - **Accommodation**: Change in the curvature of the lens that enables you to focus on nearby objects. ### What is happening with the lens? - **Emmetropia**: Light rays are focused on the retina and no corrective lens is required. The eye is relaxed and no corrective lens is required. -**Accommodation**: Ciliary muscles contract, suspensory ligaments slacken, and the lens takes on a more convex (thicker) shape. Light is refracted more strongly and focused onto the retina (near point of vision: the closest an object can be and still come into focus). ### What is a disease of the lens? - **Cataracts**: Clouding of the lens. Lens fibers darken with age, fluid-filled bubbles and clefts filled with debris appear between the fibers. It can be induced by diabetes, smoking drugs, UV radiation, and certain viruses. - **Glaucoma**: Elevated pressure within the eye due to obstruction of the scleral venous sinus and improper drainage of aqueous humor (death of retinal cells due to compression of blood vessels and lack of oxygen). ### What produces aqueous humor? - **Secreted by the ciliary body** into the posterior chamber. **Reabsorbed by the scleral venous sinus**. Aqueous humor is serous fluid. ### What disease is associated with overproduction of aqueous humor? - **Glaucoma**. ## What is the pathway of light through the retina? - Light passes through the lens to form a tiny, inverted image on **the retina**. **Photoreceptor cells** in the retina absorb light and generate an electrical signal. - **Rods and cones**: Produce visual images. - **Bipolar cells (first-order neurons)** have dendrites that synapse with rods and cones and axons that synapse with **ganglion cells**. - **Ganglion cells** (second-order neurons) are the largest neurons in the retina and are arranged in a single layer next to the vitreous body. They synapse on bipolar cells. - **Ganglion cells** form the **optic nerve** (some ganglion cells absorb light with **melanopsin** and transmit signals to the brainstem: detect light intensity for pupil control and circadian rhythms; don't contribute to visual image). - **Neural convergence and information processing** occurs in the retina before signals reach the brain. - The optic nerve contains only 1.2 million nerve fibers. ### What cells are for color vision? - **Cone cells**. There are about 6.5 million cones containing **photopsin (iodopsin)**. Photopsin contains different amino acid sequences that determine the wavelengths of light absorbed. ### What cells are for night vision? - **Rod cells**. There are about 130 million rods, which are modified calcium specialized to absorb light. They consist of: - **Outer segment**: Contains a stack of 1,000 membranous discs studded with globular protein, the visual pigment **rhodopsin** (visual purple). - **Inner segment**: Contains organelles sitting atop the cell body with the nucleus. ### What cells produce action potentials? - **Ganglion cells**. ### What is the fovea? - Contains only 4,000 tiny cone cells (no rods). No neural convergence and each foveal cone cell has a **"private line to the brain"**. Small depression within the retina where visual acuity is the highest. Acts to further focus light. # Anterior/ Posterior Pituitary - **Pituitary gland**: Suspended from the hypothalamus by a stalk (**infundibulum**). - It is housed in the sella turcica of the sphenoid bone and is the size and shape of a kidney bean. ## Anterior pituitary (adenohypophysis) - Develops from the roof of the mouth (outgrowth of the pharynx; 2/4s of the pituitary). ## Posterior pituitary (neurohypophysis) - Downgrowth from the brain (1/4 of the pituitary). - The anterior pituitary gland has no nervous connection to the hypothalamus but is linked to it by a complex of blood vessels (**hypophyseal portal system**). - The posterior pituitary gland is not a true gland but is nerve tissue (the hypothalamus secretes hormones that are stored in the posterior pituitary until released into the blood). ## Posterior Pituitary Hormones: 1. **Oxytocin (OT):** Transported by the hypothalamo-hypophyseal tract. - Stimulated by stretching of the cervix during childbirth and infant suckling. - Causes stronger contraction of the uterine muscle and milk ejection - **Targets**: Uterus and mammary glands. 2. **Antidiuretic hormone (ADH):** Transported by the hypothalamo-hypophyseal tract. - Stimulated by rising solute concentration in the blood. - Causes increased water retention. - Also called **vasopressin** because it can cause vasoconstriction. - **Targets**: Kidneys. ## Anterior Pituitary Hormones: 1. **Follicle-stimulating** **hormone (FSH)**: Stimulated by the release of GnRH from the hypothalamus. - Stimulates secretion of ovarian sex hormones, development of follicle, and sperm. - **Targets**: Gonads (testes and ovaries). 2. **Luteinizing hormone (LH):** Stimulated by release of GnRH from the hypothalamus - Stimulates ovulation, stimulates corpus luteum to secrete progesterone, and stimulates testes to secrete testosterone. - **Targets**: Gonads (testes and ovaries). 3. **Thyroid stimulating hormone (TSH)**: Stimulated by the release of TRH from the hypothalamus. - Stimulates the synthesis and secretion of T3 and T4 - Metabolic rate also stimulated. - **Targets**: Thyroid gland 4. **Adrenocorticotropic hormone (ACTH)**: Stimulated by the release of CRH from the hypothalamus. - Stimulates the adrenal cortex to secrete glucocorticoids (steroids) (primarily cortisol for fight or flight). - **Targets**: Adrenal gland 5. **Prolactin (PRL)**: Stimulated by secretion of PRH from the hypothalamus. - Stimulates mammary glands to synthesize milk after birth; enhances secretion of testosterone by testes. - Causes milk production (hypothalamus regulates lactotroph cells which produce prolactin). - **Targets**: Mammary glands 6. **Growth hormone (GH)**: Stimulated by release of GHRH from hypothalamus. - Stimulates mitosis and cellular differentiation. - Stimulates liver to produce insulin like growth factors. - **Targets**: Skeletal and cardiac muscle, adipose, liver, bone, and cartilage ## Acromegaly: - Thickening of bones and soft tissues in adults, especially in hands, feet, and face. ## Releasing and inhibiting hormones that stimulate the Ant. Pituitary - **Thyrotropin-releasing hormone (TRH)**: Promotes secretion of thyroid-stimulating hormone (TSH) and prolactin (PRL). - **Targets**: Anterior pituitary - **Corticotropin-releasing hormone (CRH)**: Promotes secretion of adrenocorticotropic hormone (ACTH). - **Targets**: Anterior pituitary - **Gonadotropin-releasing hormone (GnRH)**: Promotes secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). - **Targets**: Anterior pituitary - **Growth hormone-releasing hormone (GHRH)**: Promotes secretion of growth hormone (GH). - **Targets**: Anterior pituitary - **Prolactin-inhibiting hormone (PIH)**: Inhibits secretion of prolactin. - **Targets**: Anterior pituitary - **Somatostatin**: Inhibits secretion of growth hormone (GH) and thyroid-stimulating hormone (TSH) by the anterior pituitary. - **Targets**: Anterior pituitary # Endocrine vs Exocrine Glands: - **Receptors**: Protein or glycoprotein molecules that are either on the plasma membrane, in the cytoplasm, or in the nucleus. They act like switches, turning on metabolic pathways when hormones bind to them. - **Hormones**: Chemical messengers that travel in the bloodstream to other tissues and organs and stimulate physiological responses in cells of another tissue or organ, often a considerable distance away (1 of the 4 principal mechanisms of cell-to-cell communication). - **Gap junctions**: Pores in cell membranes allowing signaling molecules, nutrients, and electrolytes to move from cell to cell (1 of the 4 principal mechanisms of cell-to-cell communication). - **Neurotransmitters**: Released from neurons to travel across a synaptic cleft to a second cell (1 of the 4 principal mechanisms of cell-to-cell communication). - **Paracrine (local hormones)**: Secreted into tissue fluids to affect nearby cells (1 of the 4 principal mechanisms of cell-to-cell communication). - **Endocrine glands**: Secrete products (hormones) into the bloodstream. - **Exocrine glands**: Secrete products into ducts which empty into body cavities or the body surface (sweat, oil, mucous, and digestive glands). ## How the Hypothalamus Regulates Hormone Release - The hypothalamus regulates the rate of hormone release from the anterior pituitary. - The **anterior lobe** is controlled by **releasing and inhibiting hormones** from the hypothalamus. - **The neuroendocrine reflex**: Hormone release in response to nervous system signals (suckling infant—stimulates nerve endings—hypothalamus—posterior lobe—oxytocin—milk ejection). - **Feedback loops (negative)**: Increased target organ hormone levels inhibit the release of hormones. - **Feedback loops (positive)**: Increased target organ hormone levels promote release of more hormones. ## Negative Feedback Loop for the Thyroid - Low levels of T3 and T4, or a low metabolic rate, stimulate the release of **TRH** (carried by the hypophyseal portal veins to the anterior pituitary gland). This, in turn, stimulates the release of **TSH** (stimulated by thyrotroph cells). - **TSH** released into the blood stimulates **thyroid follicular cells**. The thyroid follicular cells release **T3 and T4** into the blood. - **Elevated T3** inhibits the release of **TRH and TSH** by thyroid follicular cells. ### What is the difference between positive and negative feedback? - **Negative feedback**: A decrease in blood levels, which causes receptors in the hypothalamus and thyroid cells to be activated to secrete more of the missing hormone, which increases blood levels of that hormone. - **Positive feedback**: A hormone stimulates the release of more of itself. ## Pathological Conditions Associated with the Human Growth Hormone - **Hypersecretion** of growth hormone causes acromegaly and problems in childhood or adolescence, like **gigantism** (hypersecretion) or **dwarfism** (hyposecretion). ### How GH affects blood glucose levels - **Normal blood glucose level** is ~90mg/100ml - **Low blood sugar (hypoglycemia)** stimulates the release of **GHRH** from the hypothalamus - This causes the anterior pituitary to release more hGH, which in turn causes more glycogen to be broken down into glucose by **liver cells**. - **High blood sugar (hyperglycemia)** stimulates the release of **GHIH** from the hypothalamus - This causes the release of less hGH from the anterior pituitary, which means glycogen doesn't break down glucose, and blood glucose concentration remains high. - **Excess growth hormone** raises blood glucose concentration. The pancreas then releases insulin continually. Eventually, beta-cell burnout causes **diabetes mellitus**. ### Major Physiological Connections that GH has with Other Hormones Associated with Growth and Development - **Growth hormone (GH)**: - **Induces the liver to produce growth stimulants.** - **Protein synthesis increases**: Boosts transcription of DNA, production of mRNA, amino acid uptake into cells, and suppresses protein catabolism. - **Lipid metabolism increases**: Fat catabolized by adipocytes (protein-sparing effect), which provides energy for growing tissues. - **Carbohydrate metabolism**: Glucose-sparing effect, mobilizes fatty acids, reduces dependence of most cells on glucose so it will not compete with the brain, keeps blood glucose levels high. - **Electrolyte balance**: Promotes sodium, potassium, and chlorine retention by the kidneys, enhances calcium absorption in the intestine and makes these electrolytes available to the growing tissues - **Declines gradually with age**: Lack of protein synthesis contributes to aging of tissues and wrinkling of the skin. - **Insulin-like growth factors (IGF-1)**: Have a longer half-life (about 20 hours) than the normal GH (about 6-20 minutes), so it prolongs the action of GH. - **Widespread effects on body tissues**: Stimulates mitosis and cell differentiation (cartilage, bone, muscle, and fat). # Pineal Gland - **Pineal gland**: Known as the "third eye". - Attached to the roof of the third ventricle. - Undergoes involution (shrinkage) after age 7 (peaks between ages 1-5). - May synchronize circadian rhythms of daylight and darkness. # Melatonin - **Synthesizes melatonin**: "Hormone of darkness". - **Monoamine**: Derived from serotonin. - **Fluctuates seasonally** with changes in day length. - **May regulate the timing of puberty in humans**. - **Seasonal affective disorder (SAD)**: Occurs in winter or northern climates when days are short. - **Symptoms** include: Depression, sleepiness, irritability, and carbohydrate cravings. - **Cause**: Overproduction of melatonin. - **Treatment**: 2-3 hours of exposure to bright light each day (phototherapy). Symptoms similar to symptoms for PMS. # Thymus: - Bilobed gland located superior to the heart. - Plays a role in three systems: Endocrine, lymphatic, and immune. - Shrinks after puberty. - **Site of maturation of T cells (type of WBC)**: Important in the immune defense - **Secretes hormones** that stimulate development of other lymphatic organs and activity of T lymphocytes. # Thyroid Gland - Located superior to the trachea, butterfly-shaped gland. - Secretes hormones **T3 and T4**. **Functions of T3 and T4**: - Increase metabolic rate, oxygen consumption, increase heat production, appetite, growth hormone secretion (promotes growth and development), and alertness (quicker reflexes). - TSH released from the anterior pituitary stimulates T3 and T4 release by thyroid follicular cells. # Parafollicular Cells - Also known as **C or clear cells**. - Secrete **calcitonin**. **Functions of Calcitonin**: - Stimulates osteoblast activity, calcium deposition, and bone formation. - Tones down levels of calcium (stimulated by rising calcium levels in blood). - Targets: Kidneys, bones, and the small intestine. - Decreases calcium reabsorption, inhibits osteoclast activity, and decreases calcium absorption. - **Calcitonin antagonizes the parathyroid hormone**. ## Thyroid Diseases: - **Goiter**: Any pathological enlargement of the thyroid gland. Common in inland areas where soil lacks iodine. - **Endemic goiter**: Caused by iodine deficiency- no TH, no feedback, and increased TSH stimulates hypertrophy. ### What is hypothyroidism? - Hyposecretion present at birth (formerly **cretinism**: Causes stunted growth, brain damage, and can be treated with oral thyroid hormone). - Caused by decreased TH. - **Myxedema**: Caused by decreased TH; the adult hypothyroidism. Causes low metabolic rate, sleepiness, weight gain, constipation, and dry skin. - **Grave's disease**: An autoimmune disorder which is caused by increased TH. Symptoms include irritability, muscle weakness, sleeping problems, fast heartbeat, poor tolerance of heat, diarrhea, pretibial myxedema, and eye bulging\. # Parathyroid Gland - Secretes **parathyroid hormone (PTH)** when calcium levels drop. - PTH increases blood calcium levels, increases osteoclast activity, decreases urinary excretion of calcium, and promotes the synthesis of the hormone **calcitriol** by the kidneys. - **Calcitriol** increases calcium resorption in the small intestine and increases calcium reabsorption from the skeleton. - **High or low blood levels of calcium stimulate the release of different hormones.** - **PTH**: Stimulated by low levels of calcium. - **CT (calcitonin)**: Stimulated by high levels of calcium. ## What is hyperparathyroidism? - Excess PTH secretion. - Caused by a parathyroid tumor. - Bones become soft, fragile, and deformed. - Calcium and phosphate blood levels increase. - Too much **PTH** causes too much action in osteoclast activity; calcitonin can't keep up with the increase in blood calcium. ## What is hypoparathyroidism? - Surgical excision during thyroid therapy. Fatal suffocating spasms of the muscles of the larynx in 3-4 days due to rapid decline in blood calcium. - Normal levels of **calcitonin** would tone blood calcium levels down too low, and no mechanism could increase it. # Adrenal Gland - Sits on top of each kidney. - **Adrenal medulla (inner portion)** 10-20% of the gland, has dual nature, acting as an endocrine gland and sympathetic ganglion of the SNS. - **Consists of chromaffin cells**, which are modified sympathetic postganglionic neurons and have no dendrites or axons. - **Adrenal medulla releases catecholamines** (epinephrine, norepinephrine), and some dopamine directly into the bloodstream when stimulated by fear, pain, or stress. ## Three Layers of Adrenal Cortex: 1. **Zona Glomerulosa (thin, outer layer)**: Cells arranged in rounded clusters. - Secretes **mineralocorticoids**: Regulates the body’s electrolyte balance. **Salt**. - **Aldosterone**: Stimulates sodium retention and potassium excretion. - Helps maintain blood volume and blood pressure. - Part of the renin-aldosterone-angiotensin system (RAAS). - **Targets**: Kidneys and is stimulated by ACTH. 2. **Zona Fasciculata (thin, middle layer)**: 3/4 of the cortex. Cells arranged in parallel cords separated by capillaries. - **Secretes glucocorticoids**: **Sugar**. - **Cortisol hormone**: Helps the body adapt to stress and repair tissues. - **Anti-inflammatory effect** (hydrocortisone). - Regulates glucose. - Released from amino acids from muscle and fatty acids from adipose tissue. - **Targets**: Most body cells and is stimulated by ACTH. - Excessive glucocorticoid use suppresses the immune system. 3. **Zona Reticularis (narrow, inner layer)**: Cells in branching networks. - **Secretes sex steroids**: **Sex**. - **Androgens**: Male sex steroids: Testosterone and DHT (conversion of testosterone; development of pubic hair and female libido). - **Estradiol**: Mainly estrogen produced (small quantity)—important after menopause due to ovaries no longer functioning. ## Adrenal Medulla: - Increases blood pressure, heart rate, blood flow to muscles, pulmonary airflow, and metabolic rate. - Decreases digestion and urine production—decreased parasympathetic nervous system activation. - **Glucose-sparing effect**: Epinephrine inhibits insulin secretion, which causes muscle cells to absorb glucose from the blood to increase alertness and prepare the body for physical activity. # Stress Response - Stress is caused by any situation that upsets homeostasis (injury, surgery, infection, intense exercise, pain, grief, depression, or anger). - **General adaptation syndrome**: The consistent way the body reacts to stress; occurs in three stages. ## Stages