A&P test 3

Sensory –approx 12 questions

Receptor types (free nerve endings, proprioceptors, etc) and adequate stimulus

Chemo, mechano, photoreceptors, nociceptors, thermoreceptors

• Free Nerve endings 

  • the simplest receptors, characterized by bare nerve endings that respond to a variety of stimuli, including pain, temperature, and rough touch

  • Adequate Stimuli: Pain (nociceptors), temperature (thermoreceptors), and mechanical stimuli

• Encapsulated Nerve Endings

  • These receptors are more specialized and sensitive, with nerve endings enclosed in connective tissue

  • Examples: Meissner's corpuscles (touch), Pacinian corpuscles (pressure and vibration), Ruffini endings (stretch), and Golgi tendon organs (muscle tension)

  • Adequate Stimuli: Touch, pressure, vibration, stretch, and muscle tension

• Specialized Receptor Cells

  • These are distinct structures associated with other tissues, like photoreceptors in the eyes

  • Examples: Photoreceptors (rods and cones in the eye), chemoreceptors (taste and smell), and osmoreceptors (detecting osmotic pressure). 

  • Adequate Stimuli: Light (photoreceptors), chemicals (chemoreceptors), and osmotic pressure (osmoreceptors)

• Function/Modality Receptors

• Mechanoreceptors:

  • Detect physical stimuli like pressure, vibration, touch, and stretch. 

  • Examples: Meissner's corpuscles, Pacinian corpuscles, Merkel's discs, and Ruffini endings. 

  • Adequate Stimuli: Mechanical stimuli (pressure, vibration, touch, stretch)

• Thermoreceptors:

  • Detects changes in temperature. 

  • Examples: Free nerve endings. 

  • Adequate Stimuli: Temperature changes. 

• Nociceptors:

  • Detecting painful stimuli. 

  • Examples: Free nerve endings. 

  • Adequate Stimuli: Painful stimuli (extreme temperatures, pressure, chemicals)

• Chemoreceptors:

  • Detect chemical stimuli. 

  • Examples: Taste receptors, olfactory receptors. 

  • Adequate Stimuli: Chemical stimuli (taste, smell). 

• Proprioceptors:

  • Detect body position and movement. 

  • Examples: Muscle spindles, Golgi tendon organs. 

  • Adequate Stimuli: Muscle length and tension

Special senses vs general senses

• Special Senses:

  • Organs:

    • These senses rely on specialized organs to detect stimuli:

    • Vision: Eyes 

    • Hearing and Balance: Ears (auditory and vestibular systems) 

    • Taste: Tongue (taste buds) 

    • Smell: Nose (olfactory system) 

  • Receptors:

    • The specialized organs contain complex receptors that are responsible for detecting specific stimuli. 

  • Processing:

    • Information from special senses is processed via cranial nerves, which transmit signals to the brain

• General Senses:

  • Receptors:

    • These senses are detected by receptors that are widely distributed throughout the body, particularly in the skin, but also in muscles, blood vessels, and internal organs. 

  • Types of General Senses:

    • Touch: Pressure, vibration, and other tactile stimuli. 

    • Pain: Nociception, detected by nociceptors. 

    • Temperature: Thermoreceptors detect changes in temperature. 

    • Proprioception: Sense of body position and movement. 

  • Processing:

    • General sensory information is processed via spinal nerves, which transmit signals to the brain

Taste sensations, Smell, Sensory adaptation

• Taste 

  • relies on specialized sensory cells (taste receptor cells) within taste buds located on the tongue, along the roof and back of the mouth. 

  • These taste cells detect molecules in food, responding to five basic taste qualities: sweet, sour, salty, bitter, and umami

• Smell

  • the sense of smell, depends on detecting airborne molecules (odorants) that bind to Specialized cells in the nose

  • Smell and the brain:

    • Olfactory signals travel directly to the olfactory cortex, and then to the frontal cortex and the thalamus, a different path from most other sensory information. 

• Sensory Adaptation

  • the process by which our senses become less sensitive to a constant stimulus over time. 

  • Examples: you might initially notice the smell of a perfume, but after a while, you become less sensitive to it. 

  • Adaptation mechanisms: Can occur at the level of the sensory receptors (peripheral adaptation) or within the brain (central adaptation)

Eye structure and function, Distinguish b/w rods and cones, Distinguish b/w blind spot and fovea centralis, Accessory structures for the eye, visual pathway, tunics and functions

• Eye Structure and Function

  • Cornea:

    • The transparent, outermost layer of the eye that helps focus light entering the eye. 

  • Iris:

    • The colored part of the eye that controls the amount of light entering the eye by adjusting the size of the pupil. 

  • Pupil:

    • The opening in the center of the iris that allows light to enter the eye. 

  • Lens:

    • A transparent, flexible structure behind the iris that further focuses light onto the retina. 

  • Retina:

    • The light-sensitive layer at the back of the eye that converts light into electrical signals. 

  • Optic Nerve:

    • The nerve that carries the electrical signals from the retina to the brain for processing. 

  • Sclera:

    • The tough, white outer layer of the eye that protects the internal structures. 

  • Choroid:

    • A layer of tissue between the sclera and retina that nourishes the retina and absorbs excess light. 

  • Ciliary Body:

    • A ring of tissue behind the iris that produces the aqueous humor and controls the shape of the lens. 

  • Vitreous Humor:

    • A transparent, jelly-like substance that fills the space between the lens and retina, helping to maintain the eye's shape. 

  • Aqueous Humor:

    • A clear, watery fluid that fills the space between the cornea and lens, nourishing the cornea and lens

  • Macula:

    • A small, central area of the retina responsible for sharp, detailed vision. 

  • Fovea:

    • The center of the macula, where the highest concentration of photoreceptor cells (cones) is located, providing the sharpest vision. 

  • Rods and Cones:

    • Specialized light-sensitive cells in the retina that detect light and color, respectively. 

  • Optic Disc:

    • The point where the optic nerve leaves the eye, resulting in a blind spot where there are no photoreceptors

• Tunics: the eye is composed of three tunics (layers): 

  • Fibrous tunic: The outermost layer, including the sclera (white of the eye) and cornea (transparent front part), provides structural support and allows light to enter. 

  • Vascular tunic: The middle layer, including the choroid (rich in blood vessels), ciliary body (produces aqueous humor), and iris (controls pupil size), nourishes the eye and regulates light entry. 

  • Neural tunic (retina): The innermost layer, containing photoreceptor cells (rods and cones), converts light into electrical signals, which are then transmitted to the brain

• Lens: Located behind the iris, the lens focuses light onto the retina, allowing for clear vision at various distances

• Aqueous and Vitreous Humors: these transparent fluids fill the eye, maintaining its shape and transmitting light. 

• Accessory Structures: Structures that support and protect the eye include eyelids, eyelashes, conjunctiva, lacrimal glands, and the muscles that control eye movement. 

Rods and Cones

• Rods:

  • Highly sensitive to light, allowing for vision in low-light conditions (scotopic vision) and peripheral vision, but do not mediate color vision.

• Cones:

  • Function best in bright light (photopic vision), enable color vision, and provide high visual acuity (sharpness)

Fovea Centralis and Blind spot

• Fovea Centralis:

  • A small area in the center of the retina with the highest concentration of cones, responsible for sharp, central vision and detailed color perception. 

• Blind Spot:

  • The point where the optic nerve leaves the eye, containing no photoreceptor cells (rods or cones), resulting in a lack of vision in that area

Visual Pathway

• 1. Retina:

  • Light activates photoreceptors (rods and cones), converting light into electrical signals.

• 2. Optic Nerve:

  • These signals travel through the optic nerve to the brain.

• 3. Optic Chiasm:

  • At the optic chiasm, some nerve fibers from each eye cross to the opposite side of the brain.

• 4. Lateral Geniculate Nucleus:

  • The signals are then relayed to the thalamus, specifically the lateral geniculate nucleus.

• 5. Visual Cortex:

  • Finally, the signals reach the visual cortex in the occipital lobe, where they are processed and interpreted as images.

Humors and associated cavities of eye

• Aqueous Humor

  • Location:

    •  Found in the anterior cavity, which is divided into two chambers:

  • Anterior chamber (between the cornea and iris)

  • Posterior chamber (between the iris and lens)

• Function:

  •  Provides nutrients to the cornea and lens, removes waste, and maintains intraocular pressure.

• Production and Drainage: 

  • Produced by the ciliary body and drained through the Schlemm's canal.

• Vitreous Humor

  • Location: 

    • Occupies the posterior cavity (also called the vitreous chamber), which is the space between the lens and the retina.

  • Function: 

    • Maintains the eye's shape, provides structural support to the retina, and allows light to pass through to reach the retina.

  • Composition: 

    • A gel-like, transparent substance that remains relatively constant throughout life.

Accessory structures of the eye: include the eyelids, conjunctiva and lacrimal (tear) glands. They protect, lubricate and support the eyeball

• Protective Structures: 

  • Eyelids: 

    • These movable folds of skin protect the eye from injury and debris. 

  • Conjunctiva:

    •  A thin, transparent membrane that covers the surface of the eyeball and lines the inside of the eyelids. 

  • Lacrimal apparatus: 

    • This includes the lacrimal gland (tear gland), lacrimal ducts, and nasolacrimal duct, which produce and drain tears. 

• Muscular Structures: 

  • Extraocular muscles: 

    • Six muscles (superior rectus, inferior rectus, medial rectus, lateral rectus, superior oblique, and inferior oblique) that control the movement of the eyeball. 

• Supporting Structures: 

  • Orbit: 

    • The bony socket that houses the eyeball and its accessory structures. 

  • Orbital septum: 

    • A fibrous membrane that separates the eyelid from the orbital contents. 

• Glandular Structures: 

  • Meibomian glands:

    • Glands located in the eyelids that secrete an oily substance that helps keep the eyes lubricated. 

  • Zeis glands:

    • Small glands at the base of the eyelashes that produce a waxy substance that protects the eyelashes from infection. 

  • Accessory lacrimal glands:

    • Small glands located in the conjunctiva that contribute to tear production. 

• Other Accessory Structures: 

  • Optic nerve: 

    • The nerve that transmits visual information from the eye to the brain. 

  • Retina:

    •  The light-sensitive layer at the back of the eye that converts light into electrical signals. 

  • Eyelashes:

    •  Hair-like structures that protect the eyes from dust and debris. 

  • Ciliary body:

    •  A muscular ring that controls the shape of the lens for focusing. 

Ear structure (inner, middle and outer ear) and function(s)

• Outer Ear:

  • Pinna (Auricle): 

    • The visible part of the ear, which gathers and funnels sound waves into the ear canal.

  • External Auditory Canal (Ear Canal): 

    • A tube that directs sound waves to the eardrum.

  • Tympanic Membrane (Eardrum): 

    • A thin, membrane-like tissue that vibrates when sound waves hit it, separating the outer and middle ear. 

• Middle Ear:

  • Auditory Ossicles:

    • Three tiny bones (malleus, incus, and stapes) that amplify vibrations from the eardrum and transmit them to the inner ear. 

  • Eustachian Tube:

    • A tube that connects the middle ear to the back of the throat, helping to equalize pressure in the middle ear. 

•  Inner Ear:

  • Cochlea:

    • A spiral-shaped, fluid-filled structure that converts sound vibrations into electrical signals.

  • Vestibular System:

    • Includes the semicircular canals and other structures that help maintain balance.

  • Auditory Nerve:

    • Transmits the electrical signals from the cochlea to the brain for interpretation as sound

Utricle and saccule f xn, semicircular canal structure(s) and function(s)

• Utricle and saccule (Otolith Organs)

  • Structure:

    • These are two membranous sacs located within the vestibule of the bony labyrinth. 

  • Function:

    • Linear Acceleration: 

      • Detects linear acceleration (straight-line movement) and head tilt relative to gravity. 

    • Spatial Orientation: 

      • Contribute to the sense of spatial orientation and head position in space. 

    • Macula:

      •  Contain sensory cells called hair cells within a structure called the macula. 

    • Otoliths: 

      • Hair cells in the macula are covered by a gelatinous cap with calcium carbonate crystals (otoconia). 

    • Utricle: 

      • Primarily detects horizontal linear acceleration and head tilts in the horizontal plane. 

    • Saccule: 

      • Primarily detects vertical linear acceleration and head tilts in the vertical plane

Nervous system-approx 12 question

• Central Nervous System (CNS):

  • Function:

    • The CNS is the body's command center, responsible for receiving, processing, and integrating information from the body and the external environment, and then initiating appropriate responses.

  • Components:

    • Brain: The brain is the primary control center, responsible for higher-level functions like thought, memory, and decision-making.

    • Spinal Cord: The spinal cord acts as a pathway for signals traveling between the brain and the rest of the body, also mediating some reflexes independently of the brain.

  • Protection:

    • The CNS is protected by the skull (for the brain) and the vertebral column (for the spinal cord), as well as by meninges and cerebrospinal fluid. 

• Peripheral Nervous System (PNS):

  • Function:

    • The PNS acts as a communication network, carrying signals between the CNS and the rest of the body, including muscles, organs, and sensory receptors. 

  • Components:

    • Somatic Nervous System: Controls voluntary movements of skeletal muscles, allowing us to move our limbs and perform conscious actions. 

• Autonomic Nervous System (ANS):

  •  Regulates involuntary functions like heart rate, breathing, digestion, and blood pressure. 

• Sympathetic Nervous System: 

  • Activated during stressful or "fight-or-flight" situations, preparing the body for action by increasing heart rate, blood pressure, and respiration. 

• Parasympathetic Nervous System: 

  • Promotes "rest-and-digest" functions, slowing heart rate, increasing digestion, and conserving energy. 

• Autonomic Nervous System (ANS) (a subdivision of the PNS):

  • Function:

    • The ANS regulates involuntary physiological processes, including heart rate, blood pressure, respiration, digestion, and sexual arousal. 

  • Divisions:

  • Sympathetic Nervous System (SNS): 

    • Prepares the body for "fight-or-flight" responses, increasing heart rate, blood pressure, and respiration, and mobilizing energy resources

    • Ganglia:

      • Paravertebral ganglia (sympathetic chain):

        • These are chains of ganglia located on either side of the vertebral column. 

        • Prevertebral ganglia: Located anterior to the abdominal aorta (e.g., celiac, superior mesenteric, inferior mesenteric ganglia). 

Fiber Length:

• Preganglionic fibers are relatively short, while postganglionic fibers are longer to reach target organs. 

Neurotransmitters:

• Preganglionic neurons release acetylcholine (ACh), and postganglionic neurons release norepinephrine (NE). 

• Parasympathetic Nervous System (PNS): 

  • Promotes "rest-and-digest" functions, slowing heart rate, increasing digestion, and conserving energy. 

Structure:

• The ANS consists of a network of nerves that extend throughout the body, including the brainstem and spinal cord, with autonomic ganglia (clusters of nerve cells) in the periphery.

• Ganglia:

  • Located near or within the target organs. 

• Fiber Length: 

  • Preganglionic fibers are relatively long, while postganglionic fibers are short. 

• Neurotransmitters: 

  • Both pre and postganglionic neurons release ACh.

Cranial nerves and functions

• Olfactory

  • Sense of smell

• Optic

  • Vision

• Oculomotor

  • Controls most eye movements, pupil constriction, and eyelid elevation

• Trochlear

  • Controls the superior oblique muscle of the eye (downward and inward rotation)

• Trigeminal

  • Sensory for face, mouth, and teeth; motor for chewing muscles

• Abducens

  • Controls the lateral rectus muscle of the eye (outward rotation)

• Facial

  • Facial expressions, taste (anterior 2/3 of tongue), and saliva production

• Vestibulocochlear

  • Hearing and balance

• Glossopharyngeal

  • Taste (posterior 1/3 of tongue), swallowing, and sensation in the throat

• Vagus

  • Controls heart rate, digestion, and breathing; sensory for throat and some viscera

• Accessory

  • Controls neck and shoulder muscles (sternocleidomastoid and trapezius)

• Hypoglossal

  • Controls tongue movements

Spinal nerve number and typical structure including plexuses

• Spinal Nerve Number and Structure:

  • Total Pairs: 31.

  • Cervical: 8 pairs (C1-C8)

  • Thoracic: 12 pairs (T1-T12)

  • Lumbar: 5 pairs (L1-L5)

  • Sacral: 5 pairs (S1-S5)

  • Coccygeal: 1 pair (Co1)

  • Mixed Nerves: 

    • Each spinal nerve is a mixed nerve, meaning it contains both sensory (afferent) and motor (efferent) fibers, as well as autonomic fibers.

  • Exit Points: 

    • Spinal nerves exit the spinal cord through the intervertebral foramina (small openings between vertebrae).

  • Root Structure: 

    • Each spinal nerve branches into two roots near the spinal cord: a dorsal root (sensory) and a ventral root (motor). 

• Spinal Nerve Plexuses:

  • Definition:

    •  Plexuses are networks of nerves where spinal nerves converge and branch out again, forming complex pathways. 

  • Cervical Plexus:

    •  Serves the head, neck, and shoulders. 

  • Brachial Plexus:

    •  Serves the chest, shoulders, arms, and hands. 

  • Lumbar Plexus:

    •  Serves the back, abdomen, groin, thighs, knees, and calves. 

  • Sacral Plexus: 

    • Serves the pelvis, buttocks, genitals, thighs, calves, and feet

Reflexes (knee jerk, withdrawal), components of the reflex arc

• Sensory Neuron:

  • This neuron transmits the sensory impulse from the receptor to the spinal cord (the integration center).

• Integration Center:

  • In the spinal cord, the sensory neuron synapses with a motor neuron (in a simple reflex) or with interneurons which then synapse with a motor neuron (in a more complex reflex).

• Motor Neuron:

  • This neuron carries the motor impulse from the spinal cord to the effector.

• Effector:

  • The effector is the muscle (or gland) that responds to the motor impulse, causing the reflex action (e.g., contraction of the quadriceps in the knee-jerk reflex or withdrawal of the limb in the withdrawal reflex). 

• Examples:

  • Knee-Jerk Reflex (Patellar Reflex):

    • Tapping the patellar tendon stretches the quadriceps muscle, stimulating muscle spindles. 

    • Sensory neurons transmit this information to the spinal cord. 

    • The spinal cord integrates the signal, and motor neurons stimulate the quadriceps, causing it to contract and extend the leg. 

    • This is a monosynaptic reflex, meaning the sensory neuron directly synapses with the motor neuron. 

• Withdrawal Reflex:

  • A painful or dangerous stimulus (like stepping on a tack) is detected by nociceptors. 

  • Sensory neurons transmit the pain signal to the spinal cord. 

  • The spinal cord integrates the signal, and motor neurons stimulate the flexor muscles of the affected limb, causing it to withdraw. 

  • This reflex is polysynaptic, involving interneurons in the spinal cord

Meninges - three protective membranes that cover the brain and spinal cord, providing protection, support, and nourishment

• Dura Mater

  •  The outermost and toughest layer

  • Structure:

    •  Composed of dense, fibrous connective tissue.

  • Function: 

    • Protects the brain and spinal cord from trauma. It also forms dural venous sinuses, which drain blood from the brain.

  • Location:

    •  Adheres to the inner surface of the skull and vertebrae.

• Arachnoid Mater

  •  The middle, web-like layer.

  • Structure:

    • Thin and delicate, with a spider-web appearance due to its network of fibers.

  • Function:

    •  Acts as a cushion, providing a protective barrier. The subarachnoid space beneath it contains cerebrospinal fluid (CSF), which further cushions the brain.

  • Location:

  •   Lies just beneath the dura mater

• Pia Mater

  • The innermost layer, directly covering the brain and spinal cord.

  • Structure: 

    • Thin and vascular, containing many blood vessels that supply nutrients to the nervous tissue.

  • Function: 

    • Provides nourishment and maintains the health of the nervous tissue.

  • Location:

    • Closely adheres to the contours (gyri and sulci) of the brain and spinal cord

Neurotransmitter types and actions (excitatory, inhibitory or both)

• Excitatory Neurotransmitters:

  • Glutamate:

    • The primary excitatory neurotransmitter in the brain, crucial for learning, memory, and cognitive functions. 

  • Acetylcholine:

    • Excitatory at the neuromuscular junction (causing muscle contraction), but can also be inhibitory in the heart, slowing heart rate. 

  • Epinephrine (Adrenaline):

    • A stress hormone that stimulates the central nervous system, contributing to the "fight-or-flight" response. 

  • Norepinephrine (Noradrenaline):

    • Plays a role in the sympathetic nervous system, influencing heart rate, blood pressure, and other functions. 

  • Histamine:

    • Involved in inflammatory responses, vasodilation, and immune responses. 

• Inhibitory Neurotransmitters:

  • GABA (Gamma-aminobutyric acid):

    • The primary inhibitory neurotransmitter in the brain, crucial for regulating brain activity and preventing overexcitation. 

  • Glycine:

    • The primary inhibitory neurotransmitter in the spinal cord, involved in controlling hearing processing, pain transmission, and metabolism. 

  • Serotonin:

    • Plays a role in regulating mood, behavior, sleep, and memory. 

  • Dopamine:

    • Can have both excitatory and inhibitory effects, depending on the receptor it binds to, and is associated with reward, motivation, and motor control

• Neurotransmitters with Both Excitatory and Inhibitory Effects:

  • Acetylcholine:

    •  it can be both excitatory (at the neuromuscular junction) and inhibitory (in the heart). 

  • Dopamine:

    • Can have both excitatory and inhibitory effects, depending on the receptor it binds to, and is associated with reward, motivation, and motor control. 

  • Norepinephrine:

    • Can elicit both excitatory and inhibitory responses in different brain regions.

Continuous conduction vs saltatory conduction

• Continuous Conduction: 

  • Occurs in: 

    • Unmyelinated axons (axons without a myelin sheath).

  • Mechanism: 

    • The action potential travels continuously along the entire length of the axon membrane, as voltage-gated sodium channels are present along the entire membrane, allowing for a continuous influx of sodium ions.

  • Speed: 

    • Relatively slow compared to saltatory conduction. 

• Saltatory Conduction: 

  • Occurs in:

    • Myelinated axons (axons with a myelin sheath). 

  • Mechanism:

    • The action potential "jumps" from one node of Ranvier (a gap in the myelin sheath) to the next, as the myelin sheath insulates the axon membrane and prevents action potential generation in the myelinated regions. 

  • Speed:

    • Much faster than continuous conduction, as the action potential only needs to be regenerated at the nodes of Ranvier, rather than along the entire membrane. 

  • Efficiency:

    • Saltatory conduction is also efficient, as voltage-gated sodium channels are only required at the nodes of Ranvier. 

Brain structure and functions including cortical areas and associated areas, Cerebellum and Midbrain functions, and Brainstem functions and vital centers

• Cerebral Cortex: The outermost layer of the cerebrum, responsible for higher-level functions like thought, memory, and language. 

  • Frontal Lobe: 

    • Involved in motor control, planning, problem-solving, and executive functions. 

  • Parietal Lobe: 

    • Processes sensory information, including touch, temperature, and spatial awareness. 

  • Temporal Lobe: 

    • Processes auditory information, language comprehension, and memory. 

  • Occipital Lobe:

    •  Processes visual information. 

• Associated Areas:

  • Basal Nuclei: 

    • Involved in motor control, planning, and coordination. 

  • Limbic System: 

    • Plays a role in emotions, motivation, and memory. 

  • Thalamus: 

    • Acts as a relay station for sensory information. 

  • Hypothalamus: 

    • Regulates body temperature, hunger, thirst, and other basic functions. 

• Cerebellum:

  • Function:

    • Coordinates voluntary muscle movements, maintains posture and balance, and plays a role in motor learning. 

  • Location:

    • Located at the back of the head, below the temporal and occipital lobes, and above the brainstem. 

• Brainstem:

  • Function: 

    • Regulates vital functions like breathing, heart rate, blood pressure, and sleep-wake cycles. 

  • Components:

    • Midbrain: 

      • Involved in motor control, particularly eye movements, and processes vision and hearing. 

    • Pons: 

      • Coordinates face and eye movements, facial sensations, hearing, and balance. 

    • Medulla Oblongata:

      • Regulates breathing, heartbeat, blood pressure, and swallowing. 

  • Location:

    •  Connects the cerebrum to the spinal cord.

Ventricles and CSF. Path of flow

• Cerebrospinal fluid (CSF) flows through the brain's ventricles and subarachnoid space

  • starting from the lateral ventricles→through the interventricular foramina→the third ventricle→then the cerebral aqueduct→ to the fourth ventricle→ and finally out through the apertures of Magendie and Luschka into the subarachnoid space

Review online assignments over the nervous system.

Endocrine-approx. 27 questions

Functions of endocrine system

• Hormone Production and Release:

  • The endocrine system is composed of glands that produce and release hormones directly into the bloodstream. 

  • These hormones act as chemical messengers, traveling throughout the body to target organs and tissues. 

  • The endocrine system regulates the release of hormones, ensuring they are present in the correct amounts and at the right times. 

• Key Functions:

  • Metabolism:

    • Hormones regulate how the body uses energy from food, influencing processes like nutrient absorption, storage, and utilization. 

  • Growth and Development:

    • Hormones play a crucial role in bone growth, tissue development, and the maturation of organs and systems. 

  • Reproduction:

    • Hormones are essential for the development and function of reproductive organs, as well as for sexual characteristics and fertility. 

  • Mood and Emotions:

    • Certain hormones, like those involved in the stress response, influence mood, emotional regulation, and behavior. 

  • Stress Response:

    • The endocrine system activates the body's stress response, releasing hormones like cortisol to help cope with stressors. 

  • Homeostasis:

    • The endocrine system works to maintain a stable internal environment, including regulating blood sugar levels, blood pressure, fluid balance, and body temperature. 

  • Sleep-wake cycle

    • The endocrine system helps regulate the sleep-wake cycle through hormones like melatonin. 

Membrane-bound, cytoplasmic, and nuclear receptors, Hormone Receptors (types,

location etc.)

• Membrane-Bound Receptors:

  • Location:

    • Found on the cell surface (plasma membrane). 

  • Hormone Type:

    • Primarily bind to peptide and protein hormones (which are typically water-soluble and cannot directly cross the cell membrane). 

  • Mechanism:

    • These receptors initiate signaling cascades, often involving G proteins or enzymes, to relay the hormone signal inside the cell. 

  • Examples:

    • G protein-coupled receptors (GPCRs), ion channel-linked receptors, and enzyme-linked receptors. 

• Cytoplasmic Receptors:

  • Location:

    • Found within the cytoplasm of the cell. 

  • Hormone Type:

    • Bind to lipid-soluble hormones (like steroid hormones) that can freely diffuse across the cell membrane. 

  • Mechanism:

    • Upon hormone binding, the receptor-hormone complex translocates to the nucleus, where it acts as a transcription factor, altering gene expression. 

  • Examples:

    • Steroid hormone receptors (e.g., estrogen, testosterone, glucocorticoid receptors). 

• Nuclear Receptors:

  • Location: 

    • Found within the nucleus of the cell. 

  • Hormone Type: 

    • Bind to lipid-soluble hormones that can freely diffuse across the cell membrane. 

  • Mechanism: 

    • Nuclear receptors are transcription factors that directly bind to DNA, regulating gene expression. 

  • Examples:

    •  Thyroid hormone receptor, vitamin D receptor, and retinoic acid receptor.

Types of hormone(s) that bind a particular type of receptor (Hormone types)

• Hormones that Bind to Membrane Receptors (Water-Soluble Hormones)

  • Characteristics: 

    • These hormones are hydrophilic (water-soluble) and cannot pass through the lipid membrane of cells.

  • Mechanism: 

    • They bind to extracellular receptors on the cell membrane, triggering second messenger pathways (e.g., cAMP, IP3) to carry out their effects

  • Examples:

    • Peptide Hormones (e.g., Insulin, Glucagon)

    • Protein Hormones (e.g., Growth Hormone, Prolactin)

    • Catecholamines (e.g., Epinephrine, Norepinephrine)

Receptor response(s) to hormones-(gate an ion channel, activate enzymes, alter

transcription)

• Ion Channel Gating

  • Receptor Type: 

    • Ligand-Gated Ion Channels (Ionotropic Receptors)

  • Mechanism: 

    • When a hormone or neurotransmitter binds to the receptor, it causes the ion channel to open or close, allowing ions (e.g., Na⁺, K⁺, Ca²⁺, Cl⁻) to pass through.

  • Effect:

    •  Rapid change in the electrical potential of the cell, leading to cellular responses like muscle contraction or neurotransmission.

  • Examples:

    • Epinephrine acting on ligand-gated channels in cardiac cells.

    • Acetylcholine binding to nicotinic receptors at neuromuscular junctions.

• Activate Enzymes

  • Receptor Type: 

    • Enzyme-Linked Receptors (e.g., Tyrosine Kinase Receptors)

  • Mechanism:

    •  Hormones bind to receptors that are directly linked to enzymes or activate intracellular enzymes through signaling pathways (e.g., cAMP, IP3). This triggers phosphorylation cascades.

  • Effect: 

    • Regulates cellular activities like metabolism, growth, and protein synthesis.

  • Example:

    • Insulin binding to its receptor activates tyrosine kinase, leading to glucose uptake

• Alter Transcription

  • Receptor Type: 

    • Intracellular Receptors (Cytoplasmic or Nuclear Receptors)

  • Mechanism:

    •  Lipid-soluble hormones diffuse through the cell membrane and bind to intracellular receptors. The hormone-receptor complex moves to the nucleus, where it binds to DNA and regulates gene transcription.

  • Effect:

    •  Long-term changes in protein production, influencing cell growth, metabolism, or stress responses.

  • Example:

    • Cortisol binding to glucocorticoid receptors to regulate stress-response genes.

    • Thyroid hormones (T3 and T4) enhance metabolic activity.

Paracrine and Autocrine signaling

• Autocrine Signaling:

  • A cell releases a signaling molecule (ligand) that binds to receptors on its own surface, triggering a response within the same cell. 

  • Think of it as a cell "talking to itself". 

  • Examples include the regulation of cell growth and differentiation by growth factors. 

  • Autocrine signaling can also play a role in cancer development and progression. 

• Paracrine Signaling:

  • A cell releases a signaling molecule that acts on nearby cells, but not the cell that released it. 

  • Think of it as a cell "talking to its neighbors". 

  • Examples include the communication between neurons in a synapse (synaptic signaling) and the regulation of inflammation by cytokines. 

  • Paracrine signaling is crucial for tissue development, wound healing, and immune responses. 

• Key Differences:

  • Target Cell: 

    • Autocrine signaling targets the same cell, while paracrine signaling targets nearby cells. 

  • Distance: 

    • Autocrine signaling occurs within the same cell, while paracrine signaling occurs between nearby cells. 

• Examples:

  • Autocrine: EGF (epidermal growth factor) signaling in epithelial cells, CD4+ T cells using interleukin (IL)-2 for proliferation and apoptosis. 

  • Paracrine: Synaptic signaling between neurons, nitric oxide signaling in blood vessels, and cytokine signaling in immune responses.

Comparison b/w endocrine and nervous system responses

• Nervous System:

  • Communication: 

    • Employs electrical signals (action potentials) and chemical signals (neurotransmitters) transmitted across synapses.

  • Speed: 

    • Rapid, acting in milliseconds to seconds.

  • Range of Effect:

    •  Localized and specific, targeting particular neurons, muscles, or glands.

  • Examples:

    •  Reflexes, muscle contractions, sensory perception.

  • Duration of Response: 

    • Short-lived, as signals are quickly deactivated. 

• Endocrine System:

  • Communication:

    •  Uses hormones, chemical messengers released into the bloodstream to travel to target cells. 

  • Speed: 

    • Slower, acting in seconds to minutes or even hours. 

  • Range of Effect:

    •  Widespread, affecting any cell with the appropriate receptor. 

  • Examples: 

    • Growth, metabolism, reproduction, stress response. 

  • Duration of Response:

    •  Long-lasting, as hormones can persist in the bloodstream and influence cells for extended periods. 

Endocrine vs exocrine glands

• Endocrine Glands:

  • Secretion Method: 

    • Endocrine glands secrete hormones directly into the bloodstream. They are also called "ductless glands" because they do not use ducts to transport their secretions. 

  • Secretions: 

    • They primarily produce and secrete hormones, which act as chemical messengers to regulate various bodily functions. 

  • Examples: 

    • Pituitary gland, thyroid gland, adrenal glands, ovaries, testes, pancreas (endocrine function). 

  • Function: 

    • The hormones released by endocrine glands travel through the bloodstream to target specific cells or organs in other parts of the body, influencing processes like metabolism, growth, reproduction, and mood. 

• Exocrine Glands:

  • Secretion Method: 

    • Exocrine glands secrete their substances through ducts onto body surfaces (e.g., skin) or into body cavities (e.g., digestive tract). 

  • Secretions: 

    • They produce and secrete a variety of substances other than hormones, such as sweat, sebum (oil), saliva, digestive enzymes, and mucus. 

  • Examples: 

    • Sweat glands, sebaceous glands, salivary glands, mammary glands, pancreas (exocrine function), stomach glands. 

  • Function: 

    • Exocrine gland secretions help with various bodily functions, including thermoregulation (sweating), lubrication (saliva, sebum), protection (mucus), and digestion (digestive enzymes

Major endocrine organs in the body

•  Hypothalamus: 

  • Located in the brain, it produces hormones that control the pituitary gland and regulates functions like sleep, temperature, appetite, and blood pressure. 

•  Pituitary Gland: 

  • Known as the "master gland," located at the base of the brain. It controls other endocrine glands and releases hormones like growth hormone, thyroid-stimulating hormone, and others that affect various bodily functions like growth and reproduction. 

• Pineal Gland: 

  • Found in the middle of the brain, it produces melatonin, a hormone that helps regulate sleep-wake cycles. 

•  Thyroid Gland: 

  • Located in the front of the neck, it plays a crucial role in metabolism and releases hormones like thyroxine. 

•  Parathyroid Glands:

  •  These glands are located on the back surface of the thyroid and regulate calcium levels in the body. 

•  Adrenal Glands:

  •  Located on top of each kidney, they produce hormones involved in stress response (cortisol, adrenaline), blood pressure regulation (aldosterone), and other functions. 

• Pancreas:

  •  Located behind the stomach, it has both digestive and endocrine functions. It produces insulin and glucagon, which regulate blood sugar levels. 

• Ovaries (in females): 

  • Located on either side of the uterus, they produce estrogen and progesterone, hormones that regulate the menstrual cycle and female sexual characteristics. 

• Testes (in males): 

  • Located in the scrotum, they produce testosterone, the primary male sex hormone, which is essential for sperm production and male sexual characteristics. 

Regulation and control of hormone secretion

• Hormone secretion is tightly regulated by complex feedback mechanisms, neural signals, and other factors to maintain homeostasis and respond to the body's needs. 

• Feedback Mechanisms:

  • Negative Feedback: 

    • This is the most common mechanism where the hormone itself, or a consequence of its action, inhibits further hormone secretion. For example, rising levels of thyroid hormones in the blood inhibit the release of thyroid-stimulating hormone (TSH) from the pituitary, thus reducing thyroid hormone production. 

  • Positive Feedback: 

    • Less common, positive feedback amplifies the initial stimulus, leading to a greater release of the hormone. An example is the surge of luteinizing hormone (LH) triggered by rising estrogen levels before ovulation, leading to the release of an egg. 

• Neural Control:

  • The nervous system can directly stimulate certain endocrine glands to release hormones.

  • For instance, stress triggers the sympathetic nervous system to stimulate the adrenal medulla to release epinephrine and norepinephrine, preparing the body for a fight-or-flight response.

  • Parasympathetic nervous system is the "rest and digest" system. It conserves energy by slowing down bodily processes, such as heart rate, breathing, and digestion.

  • The hypothalamus, part of the brain, controls the pituitary gland by releasing hormones that either stimulate or inhibit the pituitary's hormone secretion. 

• Other Factors:

  • Humoral Stimuli: 

    • Changes in the concentration of certain substances in the blood can directly trigger hormone release.

    • For example, high blood glucose stimulates the release of insulin from the pancreas, while low glucose levels stimulate glucagon release. 

  • Hormonal Stimuli:

    • Hormones from one endocrine gland can stimulate the release of hormones from another endocrine gland.

    • For example, the hypothalamus releases thyroid-releasing hormone (TRH), which stimulates the pituitary to release TSH, which then stimulates the thyroid to release thyroid hormones.

Structure/relationship b/w hypothalamus and anterior and posterior pituitary (i.e.,

capillary beds and veins that transport hormones or neurons that extend to each

region of the pituitary gland)

• Hypothalamus-Pituitary Connection:

  • are closely connected, forming a critical neuroendocrine control center. This connection allows the hypothalamus to regulate many bodily functions by controlling pituitary hormone secretion. 

• Hypothalamus and Anterior Pituitary (Adenohypophysis):

  • Hypophyseal Portal System: 

    • The anterior pituitary is connected to the hypothalamus via a specialized vascular network called the hypophyseal portal system. 

  • Primary Capillary Plexus: 

    • The system originates from the superior hypophyseal artery which branches off from the carotid arteries and supplies blood to the hypothalamus. This artery forms a primary capillary network in the hypothalamus. 

  • Portal Veins:

    •  Hypothalamic hormones (releasing and inhibiting hormones) are released into this primary capillary plexus. The capillaries then converge to form the hypophyseal portal veins that travel down the pituitary stalk. 

  • Secondary Capillary Plexus: 

    • These veins then enter the anterior pituitary, where they form a secondary capillary network surrounding the hormone-producing cells of the anterior pituitary. 

  • Hormonal Regulation: 

    • Hypothalamic hormones act on the anterior pituitary cells to either stimulate or inhibit the release of anterior pituitary hormones. 

• Hypothalamus and Posterior Pituitary (Neurohypophysis):

  • Hypothalamic-Hypophyseal Tract: 

    • The posterior pituitary is connected to the hypothalamus through a neural pathway called the hypothalamic-hypophyseal tract. 

  • Neuronal Projections: 

    • This tract consists of axons of neurosecretory cells whose cell bodies are located in the hypothalamus (specifically, the paraventricular and supraoptic nuclei). 

  • Hormone Storage and Release: 

    • These neurons synthesize hormones (oxytocin and vasopressin) in their cell bodies and then transport them along their axons to the posterior pituitary, where they are stored in axon terminals. Upon receiving appropriate signals from the hypothalamus, these hormones are then released directly into the bloodstream from the posterior pituitary. 

Gonadotropins

• are a group of hormones crucial for regulating the reproductive system in both males and females

• Key Gonadotropins:

  • Follicle-Stimulating Hormone (FSH): 

    • Essential for the development of ovarian follicles in females and spermatogenesis in males. 

  • Luteinizing Hormone (LH): 

    • Triggers ovulation and corpus luteum formation in females, and stimulates testosterone production in males. 

  • Human Chorionic Gonadotropin (hCG): 

    • Produced during pregnancy, it maintains the corpus luteum and supports early pregnancy. 

• Functions of Gonadotropins:

• In females:

  • FSH stimulates the growth and maturation of ovarian follicles.

  • LH triggers ovulation (the release of an egg) and promotes the formation of the corpus luteum.

  • hCG supports the corpus luteum in producing progesterone, which is crucial for maintaining pregnancy in its early stages. 

• In males:

  • FSH stimulates sperm production.

  • LH stimulates the production of testosterone, which is vital for sperm production and male sexual characteristics. 

• Regulation of Gonadotropin Secretion:

  • Gonadotropin-Releasing Hormone (GnRH):

    •  Released by the hypothalamus, GnRH stimulates the pituitary gland to release FSH and LH. 

  • Feedback Mechanisms:

    •  Sex hormones (estrogen, progesterone, and testosterone) exert negative feedback on GnRH secretion, regulating gonadotropin release. 

Aldosterone, thyroid hormones, calcitonin, PTH

• Aldosterone:

  • Role:

    •  Aldosterone is a steroid hormone produced by the adrenal cortex that primarily regulates sodium and potassium levels in the blood and tissues. 

  • Mechanism: 

    • It acts mainly on the kidneys, increasing sodium reabsorption (and thus water retention) and promoting potassium excretion. 

  • Regulation:

    •  Its secretion is primarily controlled by the renin-angiotensin-aldosterone system (RAAS), activated by low blood pressure or decreased sodium levels. Angiotensin II stimulates aldosterone release, and high potassium levels in the blood also trigger its secretion. 

• Thyroid Hormones:

  • Role:

    •  The thyroid gland produces thyroid hormones, including thyroxine (T4) and triiodothyronine (T3), which regulate the body's metabolism, affecting energy production, temperature, and various physiological functions. 

  • Mechanism: 

    • They increase the basal metabolic rate, oxygen consumption, and heat production. They also influence protein synthesis, carbohydrate metabolism, and lipid metabolism. 

  • Regulation:

    •  Thyroid hormone production is regulated by the hypothalamus and the pituitary gland. The hypothalamus releases thyrotropin-releasing hormone (TRH), which stimulates the pituitary to secrete thyroid-stimulating hormone (TSH). TSH then stimulates the thyroid gland to produce T4 and T3. High levels of thyroid hormones in the blood provide negative feedback to inhibit TRH and TSH release. 

• Calcitonin:

  • Role: 

    • Calcitonin, produced by parafollicular cells (C cells) in the thyroid gland, primarily regulates blood calcium levels by reducing them. 

  • Mechanism:

    •  It inhibits osteoclast activity, thereby decreasing calcium release from bones into the bloodstream. 

  • Regulation: 

    • Its release is directly stimulated by increased blood calcium levels. 

• Parathyroid Hormone (PTH):

  • Role: 

    • PTH, produced by the parathyroid glands, plays a critical role in regulating blood calcium levels by increasing them. 

  • Mechanism: 

    • It acts on bones, stimulating osteoclast activity and calcium release; kidneys, increasing calcium reabsorption and phosphate excretion; and intestines, promoting calcium absorption through vitamin D activation. 

  • Regulation:

    •  Its secretion is primarily triggered by low blood calcium levels. 

Pituitary gland structure and function

•  a small, pea-sized gland located at the base of the brain, behind the bridge of the nose. It sits in a bony cavity called the sella turcica  

• It's a crucial part of the endocrine system and often referred to as the "master gland" because it regulates many other endocrine glands and their functions.