Organs & Organ Systems

Learning Objectives

By the end of this class you should understand:

The structure of an organ and organ system How to describe the relative positions of different body parts The structure and functions of the integumentary system (skin) The concept of homeostasis and negative feedback loops How the skin is involved in regulating body temperature

Organs

• An organ is made of two or more tissues– Almost all have one or more

connective tissue layers around the outside

• An organ serves a specific overall function to regulate homeostasis in some way

• An organ works with other organs in an organ system

How Many Organs Do We Have?

• It varies widely depending on where you draw the line between an organ and an organ system– The human body has 206ish

bones. Is each one a separate organ?

– Even the number of organ systems varies depending on who you ask• Usually 11

Organ Systems

• There are 11 organ systems in the human body– Depending on how you

define them– Some scientists combine the

closely interrelated systems (e.g. musculoskeletal system)

• They are each a group of interrelated organs with similar functions

Describing Relative Position

• If a point is described in relation to a reference point, the language used must be clear and consistent– Towards the front/back: Anterior/posterior– Higher/lower: superior/inferior– Towards the middle/side: medial/lateral– Towards/away from the skin: superficial/deep– Towards/away from the attachment point of a

limb to the body: proximal/distal

Integumentary System

• The integumentary system consists of your skin and skin appendages– Can you name all four?

• We will use this as a model organ and model organ system– Note the different types of

tissue found throughout the organ

Skin• The skin consists of two

layers:– The epidermis (outer part)

comprised mostly of epithelial tissue

– The dermis (inner part) comprised mostly of connective tissue and blood vessels

• The skin has a layer below called the hypodermis which is most of the body’s fat reserves

Epidermis• The epidermis

consists of keratinocytes and melanocytes– Keratinocytes are

filled with a tough protein called keratin

– Melanocytes produce a pigment called melanin that colors the keratinocytes

Skin Stem Cells• Keratinocyte stem cells (basal cells) live at the

bottom of the epidermis, close to the blood supply of the dermis– They are constantly undergoing mitosis

• Some of the cells become adult keratinocytes and slowly shrivel up and die and become tough– Keratin is also the protein in your hair and nails

Melanin

• Since skin is exposed to UV light which can alter DNA, the skin cells need to be protected

• Melanin is a dark pigment that absorbs UV light

• Melanin is produced by melanocytes and coats the nuclei of all stem cells and fills the cytoplasm of the keratinocytes

• Failure to produce melanin results in albinism (being an albino)

Dermis

• The dermis makes up most of the mass of the skin– The dermis provides the

skin with its toughness and flexibility

– The dermis is also where the appendages of the skin grow from

– The dermis also has a lot of blood vessels

The Integument

Thermoregulation

• The skin is the key to maintaining body temperature– Heating: arrector pili (smooth muscles) raise

goosebumps– Cooling: sweat is produced to evaporate for

cooling

• Blood is flushed to skin for cooling or pulled away to conserve heat

• Controlled by hypothalamus in brain

Negative Feedback Loop

Homeostasis

• Homeostasis is maintained by negative feedback loops– Positive feedback loops

are self-amplifying and dangerous if not controlled

• Thermoregulation is just one example of these negative feedback loops

Thermoregulation

Organ Systems

• Organ systems contain one or more negative feedback loops to keep the body in homeostasis– Hunger, thirst, blood pressure, pH, etc– Most of these are controlled by the

hypothalamus!

• We will be learning more of these feedback loops in the future

But not yet!

• At least not until after exam 1• See you next week!