More DAT Anatomy

skeletal muscles

moves body, supports posture, and temperature

multi-nucleated

striated with sarcomeres

voluntary movements

cardiac muscle

contracts heart to pump blood

in walls of heart

one nuclei

striated with sarcomeres

involuntary

intercalated disks:

• desmosomes: hold cells together

• gap junctions: connect cytoplasm and allow ion exchange

smooth muscle

aids organ systems, gastrointestinal, digestive and circulatory systems

one nuclei

nonstriated

involuntary

order of skeletal muscle components

skeletal muscle → muscle fascicles → muscle fibers → myofibrils

skeletal muscle component

largest bundle

surrounded by epimysium

composed of muscle fascicles

muscle facicles component

surrounded by perimysium

muscle fibers component

muscle itself, surrounded by endomysium

cell membrane is sarcolemma

myofibrils

smallest bundle

surrounded by sarcoplasm composed of contractile proteins

sarcomeres

functional unit of muscle fiber, located in myofibrils

contains myofilaments = protein filaments

actin = thin

myosin = thick

neuromuscular junction

connection between motor neuron and muscle cell

steps of a muscle contration

1. action potential reaches end of axon, Ach released int neuromuscular junction

2. ach bunds ligand-gated channels Na+ channels, causes excitatory response

3. if threshold reached, action potential is created

4. action potential goes doen T-tubules, triggeres sarcoplams reticulum to release Ca2+

5. Ca2+ binds troponin C, stimulates powerstroke

6. muscle fiber shortens and muscle contracts

troponin C

contractile filament that is a regulatory protein

binded to actin doesnt allow myosin to bind

tropomyosin

contractile filament that is a regulatory protein

doesnt allow myosin to bind to actin

t-tubules

pouches in sarcolemma

sarcoplasmic reticulum

regulates Ca2+

sarcoplams

cytoplasm of skeletal and cardiac cells

Cross-Bridge Cycle Steps

1. ADP-bound myosin head is cocked and ready to bind to actin. tropomyosin blacks muscle contraction, high energy state

2. Ca2+ binds troponin C and exposes the site for myosin binding

3. power stroke occurs, myosin head bends and pulls actin toward center of sarcomere, shortens it and contracts muscle

4. ADP and phosphate released, myosin back in low energy state

5. if more calcium present another cross-bridge forms

6. no Ca2+, tropomyosin covers binding site

z-line

ends of sarcomeres

m-line

middle of sarcomere

I band

part of sarcomere with only actin

H band

part of sarcomere with only myosin

A band

spans the length of myosin and actin myosin overlap

during contraction of muscle: I and H bands shrink, A stays the same

small motor unit

only a few muscle fibers innervated by a motor neuron

used for precise movments

large motor units

Many muscle fibers innervated by a motor neuron

powerful movements

twitch contraction

action potential spreads over a motor neuron and stimulates contraction of all the muscle fibers belonging to its motor unit

each twitch has the same size and duration

exoskeleton

external

invertebrates and all arthropods

2 protein layers

endoskeleton

internal

vertebrates

bone and cartilage

axial skeleton: central bones

appendicular skeleton: bones of appendages

long bones

cylindrical bones od sppendicular skeletonh

ematopoiesis

blood cell production

epiphysis

ends that form joints

squishy and contain red bone marrow

diaphysis

long hollow shaft

medullar cavity

within diaphysis

red bone marrow: stem cells turn into erythrocytes and leukocytes

yellow bone marrow: stem cells produce fat, bone, cartilage, muscle and can store fatm

etaphysis

neck of long boneep

epiphyseal plate

cartilage between epiphysis and metaphysis

lengthens the diaphysis through ossification

made of hyaline cartilage

periosteum

outer layer of cortical bone

cortical bone

dense outerlayer supports body weight

compact bone

osteon

functional unit, thin layered cylinders

havarsian systems

lamellae

cylindrical layers of osteons

haversian canal

tubes in the center of the osteon unit that contain blood vessels for nutrient supply “vertical”

volkmann’s canal

channels with blood vessels connect havarsian system to periosteum “horizontal”

endosteum

internal sheath of cortical bone

cancellous bone

spongy inner layer

soaks up red bone marrow via web of trabeculae

trabeculae

branching structures made of connective tissue

osteoblasts

build bone, secrete protein and utilize calcium from blood, mature into osteocytes

osteocytes

trapped within the bone matrix

part of osteons to maintain bone

osteoclasts

degrade bone, eat and absorb bone by releasing enzymes and reducing pH

release Ca2+ and phosphate back into blood

organic part of bone composition

osteoid, contains protein like collagen fibers, provides tensile strength

inorganic part of bone composition

hydroxyapetite, mineralized material embedded within the osteoid contributes to bone density and strength

parathyroid hormone

increase Ca2+ in the blood stream

stimulates osteoclasts

increase reabsorption of Ca in kidney, decreasing excretion in urine

calcitonin

decrease Ca2+ in blood stream

thyroid gland

inhibit osteoclasts

decrease reabsorption of Ca in kidney

calcitonin tones down calcium in blood

intramembranous ossification

direct bone formation within sheets of embryonic connective tissue

contains stem cells that develop into osteoblasts, osteoblasts deposit osteoid, calcifies and forms cortical bone

occurs mostly in flat bones

endochondral ossification

indirect formation, cartilage replace with bone

initial cartilage forms first, osteoid deposited and gradually replaces cartilage, osteoid calcifies forms cortical bone

most bones of the body

connective tissue

supportive matrix composed of either cells, fibers, gell like filler

fibroblasts

connective tissue resident cells secrete constituents of fibrous connective tissue, maintains and remodles matrix

fibrous connective tissue

high concentration of fibers

periosteum and endosteum

ligament

bone to bone

tendon

bone to muscle

cartilage

non-innervated

avascular

joints

meeting points between bones

vascularized and innervated

contains connective tissue

endocrine hormone

secreted directly into blood stream

paracrine hormone

secreted into neighboring cells

autocrine hormone

secreted onto the same cell which is secreting it

peptide hormones

proteins based

synthesis in rough endoplasmic reticulum

bind to cell surface receptors, cannot pass through membrane → indirect stimulation

ligand-gated receptors

receptor proteins that induce a signal transduction pathway once extracellular ligand is bound

secondary messenger

signaling molecule that is different from the originial hormone which propagated the signal

causes an intracellular effect

ex. cAMP, IP3, DAG, Ca²⁺

GCPRs (G Coupled Protein Receptors)

protein on the intracellular domain responsible for conveying intracellular signals

require activation to make a response

Receptor Tyrosine Kinases (RTKs)

twin components dimerize and cross phosphorylate in order to influence intracellular signals

IP3/DAG Pathway

regulates release of stored Ca²⁺ from endoplasmic reticulum into cell cytosol

Steps:

1. pathway is activated when appropriate ligand binds to GPCR

2. GCPR activates the associated G protein via binding one GTP molecule

3. G protein activates the enzyme Phospholipase C

4. Activated PPC cleaves lipid PIP2 into 2 separete second messengers IP3 and DAG

5. IP3 binds ligand gated Ca²⁺ channels on surface of ER

6. ER calcium channels open releasing Ca into cytosol

7. free calcium affects many pathways

steroid hormones

made from modified cholesterol molecules

produced in smooth ER

base is a 4 ring structure with different functional groups

all the hormones produced by adrenal cortex and gonads

steroid hormones from adrenal cortex

glucocorticoids

mineralocorticoids

androgenic steroids

steroid hormones from reproductive organs

progesterone

testosterone

estrogen

Steroid hormones traveling through the body

lipophilic and able to pass the membrane directly

lipid soluble

require association with water soluble proteins to travel through blood

directly bind to intracellular receptors that results in steroid-receptor complexes that bind to DNA to affect transcription

cause slow and gradual genetic change

Amino Acid Derived Hormones

propertied similar to both peptide and steroid hormones

produced in rough ER and cytosol

mainly derived from amino acid tyrosine

all hormones of the adrenal medulla and T3 and T4 adre

adrenal medulla hormones

epinephrine

norepinephrine

hypothalamus

coordinates body temperature and maintain homeostasis

regulates hormone secretion

produces its own hormones or stimulators to act on pituitary glandp

pituitary gland (hypophysis)

hormone production, storage, and release

rests right below hypothalamus

posterior and anterior portions

posterior pituitary gland

direct neuronal extension of hypothalamus

Stores and releases hormones produced by hypothalamus

antidiuretic hormone (ADH, Vasopressin)

oxytocin

ADH, Antidiuretic hormone (vasopressin)

decrease urination by increase water retention, targets nephrons, increase number of aquaporins

oxytocin

causes uterine contractions during childbirth and milk while breastfeeding

targets uterus and mammary glands

anterior pituitary gland

produces its own hormones from signals by the hypothalamus

hypophyseal portal system

connect anterior pituitary gland to hypothalamus

allows for quick diffusion through the portal vein

hormones released by the hypothalamus stimulate the anterior pituitary gland to release other hormones

hypophyseal hormones

GnRH (gonadotropin-releasing hormone): cause release of LH and FSH

TRH (thyrotropin-releasing hormones): cause release of thyroid stimulating hormone, TSH

CRH (corticotropin-releasing hormones): cause release of adrenocorticotropic hormone, ACTH

GHRH (growth hormone-releasing hormone): cause release of GHH

Hormones released following stimulation from hypothalamic-releasing hormones

FSH

LH

ACTH

TSH

Prolactin

GH

tropic hormones

target other endocrine glands for further hormone release

direct hormones

target organs directly for effects

FLAT PiG

tropic is FLAT hormones

direct is PG hormones

follicle stimulating hormone (FSH)

follicle growth in females (produce estrogen)

sperm maturation in males

Luteinizing hormone, LH

stimulates ovulation and corpus luteum (produce estrogen) in females

stimulates testosterone production in males

adrenocorticotropic hormone (ACTH)

release of glucocorticoids from adrenal gland to fight stress, increase glucose levels

Thyroid stimulating hormone, TSH

stimulates T3 and T4 production to increase metabolism

prolactin

stimulate mammary gland and milk production

growth hormone GH (somatotropin)

stimulates body cells growth and development

thyroid gland

largest endocrine gland, front of trachea

3 hormones

triiodothyronine, T3

increase metabolismreleased

release in response to TSH

negative feedback effect on TSH secretion

thyroxine, T4

same action as T3, one more iodine, convert to T3 upon cell uptake

less potent and more stable in blood for transport

calcatonin

decrease blood Ca²⁺ level

secretes by parafollicular thyroid cells (C cells)

target kidneys → increase calcium secretion

target bones → inhibit osteoclasts

thyroid conditions

hypothyroidism: undersecretion of T3, T4, reduced metabolic rate

hyperthyroidism: over-secretion, increase metabolic rate

goiter

Physical enlargement of the thyroid gland

caused by both hyper and hypothyroidism

iodine deficiency: most common cause, essential for synthesis

parathyroid gland

rest on posterior aspect of thyroid gland

parathyroid hormone (PTH): increase blood Ca, prevent excretion, stimulate osteoclasts

pancreas

both endocrine and exocrine tissuese